National Hospital Discharge Survey, 1979-1996

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Scientific Data Documentation

National Hospital Discharge Survey, 1979-1996

DSN: CC36.NHDS7996.NEWBORN
     CC36.NHDS7996.NOT.NEWBORN

 
NATIONAL HOSPITAL DISCHARGE SURVEY, 1979-1996 DATA TAPE DOCUMENTATION

This document is intended for users of the National Hospital Discharge Survey (NHDS)
multi-year data files containing all records for the 1979 to 1996 data years.  These data
files provide access to NHDS data for the years in which the 9th Revision of the
International Classification of Diseases, Clinical Modification (ICD-9-CM), has been
used for coding medical diagnoses and procedures.  However, important changes in the
survey methodology, as well as modifications of the coding system, have occurred during
the years spanned by these files.

For those who are familiar with the single-year, public use data files for NHDS, it is
important to note several major differences between the multi-year files and the
single-year files.  First, unlike the annual, single-year files, there are two distinct multi-
year files, one containing records for newborn infants only, the other containing non-
newborn records.  Second, the single-year data files include several recodes of basic
variables which are not included on the multi-year files.  Third, to save space, all blank
fields which separate data elements on the single year files have been eliminated from the
multi-year files, resulting in a different data layout.

NOTE: Separate files which contain information needed for Appendices D and E are
provided in LOTUS files on a diskette accompanying this documentation.

I.  DESCRIPTION OF THE NATIONAL HOSPITAL DISCHARGE SURVEY

INTRODUCTION.  The National Hospital Discharge Survey (NHDS) has been
  conducted continuously by the National Center for Health Statistics (NCHS) since 1965. 
  It provides data on inpatient utilization of short-stay, non-Federal hospitals in the United
  States.  The NHDS abstracts both demographic and medical information from the face
  sheets of the medical records of inpatients selected from a national sample of hospitals. 
  Based on this information, national and regional estimates of characteristics of patients,
  lengths of stay, diagnoses, and surgical and nonsurgical procedures in hospitals of various
  bed sizes and types of ownership are produced.  The survey design, sampling, and
  estimation procedures were planned to produce calendar year estimates.

  The NHDS utilizes a stratified, multi-stage probability design.  The original sample,
  drawn in 1965 and followed through 1987, was based on a two-stage sampling plan.  A
  new sample was drawn in 1988, when a three-stage sampling plan was implemented, and
  several data collection and estimation procedures were revised.  The redesign of the
  survey is important, especially for those conducting trend analyses.  That is, because the
  new survey differs from the original one in sample design, data collection, and estimation
  procedures, some of the differences between NHDS statistics based on the 1965-87
  sample and statistics based on the sample drawn in 1988 may due to the survey redesign
  rather than actual changes in hospital utilization.

  Since 1979, the International Classification of Diseases, 9th Revision, Clinical
  Modification, (ICD-9-CM), has been used for classifying diagnoses and procedures in the
  NHDS.  However, beginning in 1986, the ICD-9-CM has been modified annually. These
  modifications become effective in October of each year and are published in an
  Addendum.  Users of the NHDS who wish to conduct trend analyses or other multiple
  year studies must take into account the ICD-9-CM Addenda.  Appendix B contains the
  changes for 1986 through 1995.

  For a general description of the survey design and data collection procedures, see below. 
  For more detailed information on technical aspects of the survey, see Reference 1. 
  Publications based on the data collected in each survey year can be obtained from the
  Government Printing Office. Rates in these publications may differ slightly from rates
  which are calculated using the population estimates provided here because the population
  estimates accompanying this dataset are based on the 1990 decennial census.

HISTORY.  In 1962, the NCHS began exploring possibilities for conducting a survey to
  provide information on the utilization of the Nation's hospitals and on the nature and
  treatment of illness among the hospitalized population.  A national advisory group was
  established, and NCHS undertook planning discussions with other officials of the Public
  Health Service.  Hospitalization material from the Survey Research Center of the
  University of Michigan, the American Hospital Association, and the Professional
  Activities Study was examined and evaluated.  In 1963, a study by the School of Public
  Health of the University of Pittsburgh under contract to the NCHS demonstrated the
  feasibility of an NHDS type of program.  An additional pilot study using enumerators
  from the Bureau of the Census was conducted in late 1964 and confirmed the University
  of Pittsburgh's findings.  Finally, with advice and support from the American Hospital
  Association, the American Medical Association, individual experts, other professional
  groups, and officials of the U.S. Public Health Service, the NCHS initiated the National
  Hospital Discharge Survey in 1964.

SOURCE OF THE DATA.  The National Hospital Discharge Survey (NHDS) covers
  discharges from noninstitutional hospitals, exclusive of Federal, military, and Veterans
  Administration hospitals, located in the 50 States and the District of Columbia.  Only
  short-stay hospitals (those with an average length of stay for all patients of less than 30
  days) or those whose specialty is general (medical or surgical) or children's general are
  included in the survey.  These hospitals must also have six or more beds staffed for
  patient use.  These criteria, used since the survey redesign in 1988, differ slightly from
  those used under the old design.  Prior to 1988, hospitals with an average length of stay of
  30 days or more were excluded, regardless of specialty.  However, the term "short-stay"
  continues to be used because 98 percent of the hospitals in the NHDS universe fall into
  this category.

  The original universe for the survey consisted of 6,965 short-stay hospitals contained in
  the 1963 National Master Facility Inventory of Hospitals.  This list was updated
  periodically from lists of hospitals provided by the American Hospital Association. 
  When the survey was redesigned in 1988, the NHDS sampling frame consisted of
  hospitals that were listed in the April 1987 SMG Hospital Market Tape (Reference 2),
  met the above criteria, and began accepting patients by August 1987.  Table 1 shows the
  number of hospitals in the NHDS universe and sample, as well as the approximate
  number of sampled abstracts and estimated number of discharges, for each year from
  1979 to 1996.  Beginning in 1984, data on the universe of short-stay non-Federal
  hospitals were obtained from the American Hospital Association, instead of the Master
  Facility Inventory of Hospitals.

SAMPLING DESIGN.  The purpose of the NHDS redesign in 1988 was to provide
  geographic comparability with other surveys conducted by the NCHS; to update the
  sample of hospitals; and to use data already available in automated systems.  While the
  redesign added some complexity to the sampling plan of the NHDS, the old and new
  designs remain quite similar.  Under both designs, all hospitals with 1,000 or more beds
  were selected with certainty.  In the redesigned NHDS sample, all hospitals with 40,000
  or more discharges annually were also certainty hospitals.  In both designs, discharges
  were selected within hospitals according to a systematic sampling procedure.

TABLE 1.  Number of  Hospitals in Universe and Sample, Participation and Respondent Counts,
          Approximate Total Number of Sampled Discharge Abstracts, and Estimated Number of 
          Patients Discharged, NATIONAL HOSPITAL DISCHARGE SURVEY, 1979-1996

DATA YEAR	NUMBER OF HOSPITALS IN UNIVERSE	NUMBER OF HOSPITALS IN SAMPLE	NUMBER OF OUT-OF-SCOPE HOSPITALS	NUMBER OF REFUSAL HOSPITALS	NUMBER OF RESPONDING HOSPITALS	APPROXIMATE NUMBER OF SAMPLED ABSTRACTS	ESTIMATED NUMBER OF DISCHARGES (in thousands)
						[includes newborn infant records]	[excludes newborn infants]
1979	8,017	544	48	80	416	215,000	36,747
1980	8,017	544	52	72	420	224,000	37,832
1981	8,080	550	51	71	428	227,000	38,543
1982	8,080	550	53	71	426	214,000	38,594
1983	8,130	553	57	78	418	206,000	38,784
1984	6,023	553	60	86	407	192,000	37,162
1985	6,007	558	62	82	414	195,000	35,057
1986	6,007	558	65	75	418	193,000	34,255
1987	6,007	558	66	92	400	181,000	33,387
1988	6,400	542	11	109	422	250,000	31,146
1989	6,400	542	16	118	408	233,000	30,947
1990	6,400	542	23	45	474	266,000	30,788
1991	6,250	528	7	37	484	274,000	31,098
1992	6,250	528	14	20	494	274,000	30,951
1993	6,250	528	15	47	466	235,000	30,825
1994	6,337	525	13	34	478	277,000	30,843
1995	6,337	525	17	42	466	263,000	30,722
1996	6,337	525	18	27	480	282,000	30,545
From 1984 to 1987, data on the universe of short-stay, non-Federal hospitals was obtained from the American Hospital Association, instead of the Master Facility Inventory of Hospitals. Beginning in 1988, the sampling frame for hospitals has been the SMG Hospital Market Database (References 2-4).

From 1984 to 1987, data on the universe of short-stay, non-Federal hospitals 
was obtained from the American Hospital Association, instead of the Master 
Facility Inventory of Hospitals.  Beginning in 1988, the sampling frame for 
hospitals has been the SMG Hospital Market Database (References 2-4).

However, the old and new designs differ in how noncertainty hospitals were selected.  
In the former, a two-stage sample was used, and in the latter, a three-stage plan was
implemented. Under the old design, the first-stage sampling units were hospitals, which
were selected within 24 bedsize-by-region strata, controlling for type of ownership and
Census geographic division.  At the second stage, discharges within hospitals were
selected by a systematic random sampling technique, using a sampling rate such that the
overall probability of selecting a discharge was approximately the same in each
hospital-size class.  In the new design, 112 PSU's from the 1985-94 National Health
Interview Survey sample were selected as first-stage sampling units. Hospitals within
PSU's were then selected at the second stage.  Strata at this stage were defined by
geographic region, PSU size, abstracting service status,  PSU, and hospital specialty-size
groups.  Within strata, hospitals were selected with probabilities proportional to their
annual number of discharges.  At the third stage, a sample of discharges was selected by a
systematic random sampling technique.  The sampling rate was determined by the
hospital's sampling stratum and the type of data collection  system (manual or automated)
used.

Note again that these changes in the design of the survey may affect trend data.  That is,
some observed differences between NHDS statistics based on the 1965-87 sample and
those based on the redesigned sample may be due to updating the sample and revising
data collection and estimation procedures rather than actual changes in hospital
utilization.  A report comparing selected estimates obtained from the old and the new
survey designs has also been published (Reference 5).

DATA COLLECTION PROCEDURES.  Originally, all data collection for NHDS was
  conducted manually within the hospital, either by hospital personnel or by Bureau of
  Census staff under contract with NCHS.  Currently, approximately 62 percent of the
  responding hospitals utilize the manual system of sample selection and data abstraction. 
  Of the hospitals using this system in 1996, about 34 percent had the work performed by
  their own medical records staff.  In the remaining hospitals using the manual system,
  personnel of the U.S. Bureau of the Census did the work on behalf of NCHS.  The
  completed forms, along with sample selection control sheets, were forwarded to NCHS
  for coding, editing, and weighting.

  Beginning in 1985, data from some hospitals was obtained from commercial abstracting
  services, state computerized data systems, or a hospital's own computer system. 
  Computer tapes from these sources contained machine-readable medical record data from
  which records were systematically sampled by NCHS.  In 1996, this method was used for
  about 38 percent of the respondent hospitals.

THE UNIFORM HOSPITAL DISCHARGE DATA SET  (UHDDS).  Starting with 1979
  data, the NHDS has followed guidelines of the Uniform Hospital Discharge Data Set
  (UHDDS) within the confines of its contractual agreement with participating hospitals. 
  The UHDDS is a uniformly defined, minimum data set  (Reference 6).  Items for the data
  set were selected on the basis of their usefulness to a broad range of organizations and
  agencies requiring hospital information, uniformity of definition, and general availability
  from medical records and abstract services.

  Both the medical abstract form used in manual data collection and the automated data
  contain items relating to the personal characteristics of the patient, including birth date or
  age, sex, race, and marital status; administrative information, including admission and
  discharge dates, discharge status, and medical record number; and medical information,
  including up to seven diagnoses and up to four surgical or nonsurgical procedures.  Since
  1977,  patient zip code, expected source of payment, and dates of surgery have also been
  collected.  The medical record number, date of birth, and patient zip code are confidential
  information and are not available to the public.  The medical abstract form (HDS-1) is
  updated periodically.

MEDICAL CODING AND EDIT.  The medical information that was recorded manually
  on the sampled patients' abstracts was coded centrally by NCHS staff, using the
  International Classification of Diseases, 9th Revision, Clinical Modification, or
  ICD-9-CM (Reference 7).  A maximum of seven diagnostic codes was assigned for each
  sampled abstract; in addition, if the medical information included surgical or nonsurgical
  procedures, a maximum of four codes for these procedures was assigned.  Since 1991, all
  of the diagnostic and procedure codes in the ICD-9-CM have been utilized.  However, for
  the years 1979 to 1990, some procedure codes were not utilized and so it is not possible
  to produce estimates for those codes.  Appendix C contains a listing of the procedures not
  coded and the year the code was first used.  It is important to note that the ICD-9-CM
  serves as a basis for classifying morbidity information on medical records, and as a tool
  for generating basic health statistics.  As it is used in the NHDS, it is not intended to
  provide a complete clinical picture of a patient.

  NHDS usually presents diagnoses and procedures in the order they are listed on the
  abstract form or obtained from abstract services, however, there are exceptions.  For
  women discharged after a delivery, a code of V27 from the supplemental classifications
  was entered as the first-listed code, with a code designating either normal or abnormal
  delivery in the second-listed position.  In another exception, a decision was made to
  reorder some acute myocardial infarction (AMI) diagnoses.  If an acute myocardial
  infarction was listed with other circulatory diagnoses and was other than the first entry, it
  was reordered to the first position.  If a code from Chapter 16 (Symptoms, Signs, and
  Ill-Defined Conditions), appeared as a first-listed code and a diagnosis appeared as a
  secondary code, the diagnosis code was moved to the first position and the symptom code
  was moved back.

  Following conversion of the information on the medical abstracts to computer tape and
  combining it with the automated data tapes, a final medical edit was accomplished by
  computer inspection and by a manual review of rejected records.  Priority was given to
  medical information in the editing.

MEASUREMENT ERRORS.  As in any survey, results were subject to nonsampling or
  measurement errors, which included errors due to hospital nonresponse, missing
  abstracts, information incompletely or inaccurately recorded on abstract forms, and
  processing errors.  In general, approximately one percent of the discharge records failed
  to include the age or sex of the patient.  If the hospital record did not state the age or sex
  of the patient, it was imputed by assigning the patient an age or sex consistent with the
  age or sex of other sampled patients with the same diagnostic code.  Beginning in 1996,
  this imputation was designed to maintain the known distribution of the age or sex
  variable.  If the dates of admission or discharge were not given, and if they could not be
  obtained from the monthly sample listing sheet transmitted by the sample hospital, a
  length of stay was imputed by assigning the patient a stay characteristic of the stays of
  other patients of the same age.  For records where the length of stay and the discharge
  month were known, a discharge day of the 20th of the month was assigned to the record,
  and the admission date was computed based on the given length of stay.  Other edit and
  imputation procedures may have been applied to data received in automated form.

SAMPLING ERRORS AND ROUNDING OF NUMBERS.  The standard error is
  primarily a measure of sampling variability that occurs by chance because only a sample
  rather than the entire universe is surveyed.  The relative standard error of an estimate
  (RSE) is obtained by dividing the standard error by the estimate itself.  When the
  resulting value is multiplied by 100, the relative standard error is expressed as a percent
  of the estimate.  The RSE is used as guide to the reliability of the estimate (see
  Presentation of Estimates below).

  Since 1988, estimates of sampling variability have been calculated with SESUDAAN or
  SUDAAN software, which computes standard errors by using a first-order Taylor series
  approximation of the deviation of estimates from their expected values.  A description of
  the software and the approach it uses was published by Shah (Reference 8).  Before 1988,
  standard error estimates were produced using a computerized routine based on a
  rigorously unbiased algebraic estimator of the variance.

  To obtain standard errors that would be applicable for a wide variety of statistics and that
  could be prepared at a moderate cost, numerous variances were calculated and a best fit
  formula was derived.  This formula, which is based on an empirically determined
  relationship between the size of an estimate, X, and its relative variance, was used to
  produce generalized variance curves. These curves provide approximations to the relative
  standard errors that are applicable to estimates of discharges, first- or all-listed diagnoses,
  all-listed procedures, and days of care, either aggregated or disaggregated by selected
  patient or hospital characteristics.

  For the years 1979 through 1987, curves are represented in tables containing estimates of
  different sizes and their approximate relative standard errors.  For the years 1988 through
  1996, tables contain parameter values which can be substituted in a mathematical formula
  (described in Appendix D) to produce approximate relative standard errors.  Instructions
  on how to use the tables and/or the parameter values are also given in Appendix D.

PRESENTATION OF ESTIMATES.  Based on consideration of the complex sample
  design of the NHDS, the following guidelines are recommended for using the 
  NHDS estimates:

  If the sample size is less than 30, the value of the estimate is 
  not reported.   

  If the sample size is 30-59, the value of the estimate is reported 
  but should not be assumed reliable.     

  If the sample size is 60 or more and the relative standard error is 
  less than 30 percent, the estimate may be reported.      

  If the sample size is 60 or more but the relative standard error is 
  over 30 percent, the estimatemay be reported but should not be assumed 
  reliable.

POPULATION ESTIMATES.  Hospital utilization rates are computed using U.S. Census
  Bureau population estimates as denominators.  Before 1981, estimates of rates of
  discharges and days of care which appeared in published reports from NCHS were
  calculated using estimates of the civilian noninstitutional population (CNP).  However,
  beginning in 1981, estimates of the civilian resident population (CRP) were used to
  calculate hospital utilization rates.  The CRP was determined to be more appropriate
  because persons in institutions, for example nursing home patients, are hospitalized when
  necessary.  A report has been published which discusses differences in discharge rates
  based on the different denominators (Reference 9).

  Files containing estimates of the civilian resident population as of July 1 of each year
  from 1979 to 1996 are provided with this documentation.   The estimates for 1980-1996
  have been adjusted based on the 1990 decennial census, and the 1979 estimates were
  adjusted based on the 1980 census.  Therefore, any rates calculated with these estimates
  may differ slightly from those which appear in published NCHS reports or those
  calculated from population estimates disseminated with the NHDS single-year data tape
  documentation.

CAUTION ABOUT MONTHLY AND SEASONAL ESTIMATES.  An important difference between the
  old and new designs is the method used to adjust for nonresponse.  The result
  of this difference is that monthly and seasonal estimates under the new design
  may be skewed.  While the effect is believed to be small, it is recommended that partial
  year estimates not be produced for 1988 and later years. The reasons for this are
  explained below.

  In the old design, weights for responding hospitals were adjusted each month to account
  for hospitals that did not respond for that month.  In the new design, the type of
  nonresponse adjustment applied depended on whether the hospital was considered a
  nonrespondent or partial respondent.  A nonresponding hospital was one which failed to
  provide at least half of the expected number of discharges for at least half of the months
  for which it was inscope.  In this case, weights of discharges from hospitals similar to the
  nonresponding hospital were inflated to account for discharges of the nonrespondent
  hospital.  However, this adjustment was performed just once, after the close out of the
  survey for the year, instead of monthly as before.

  For partially responding hospitals, one or both of two adjustments were made.  If the
  hospital provided at least half, but not all, of the expected number of abstracts for a given
  month, the weights of the abstracts actually collected for that month were inflated to
  account for the missing abstracts.  If fewer than half of the expected number of abstracts
  were provided, the weights of the abstracts provided were inflated by a factor of two, then
  another adjustment was made to account for the excess nonresponse.  In the second
  adjustment, the weights of the discharges in the hospital's respondent months were
  inflated by ratios that varied by category of first-listed ICD-9-CM diagnostic code.  This
  adjustment ratio was based on the hospital's month(s) of nonresponse and the
  month-by-month distributions of first-listed diagnostic groups among discharges from
  hospitals which responded for all twelve months.  The ratio accounts for the seasonality
  in the occurrence of the first-listed diagnostic groups for annual statistics, but not for
  partial year estimates.  As a result, monthly and seasonal estimates may be skewed. 
  While the effect is believed to be small, it is recommended that partial year estimates not
  be produced.  In the 1996 NHDS, 76 percent of the 480 responding hospitals provided
  data for all twelve months, and 95 percent provided at least 9 months of data.

HOW TO USE THE DATA FILE.  The NHDS records contain weights to allow inflation
  to national or regional estimates.  The weight for each record is found in tape location
  21-25.  To produce an estimate of the number of discharges, the weights for the desired
  records must be summed.  To produce an estimate for number of days of care, the weight
  must be multiplied by the days of care (tape location 13-16) and these products summed. 
  Estimates apply to the calendar year (January-December).   Appendix F contains
  frequencies for selected descriptive variables on the data tape.  These may be used as a
  cross-check when processing the data on the user's system.

QUESTIONS.  Questions concerning the data file should be directed to Maria Owings,
  Ph.D., Hospital Care Statistics Branch, Division of Health Care Statistics, National
  Center for Health Statistics, Presidential Building, Room 956, 6525 Belcrest Road,
  Hyattsville, Maryland  20782, (301)-436-7125.

REFERENCES
  
1. National Center for Health Statistics:  Development of the design of the NCHS
   Hospital Discharge Survey, by W. R. Simmons.  Vital and Health Statistics.  PHS Pub.
   No. 1000, Series 2-No. 39.  Public Health Service.  Washington.  U.S. Government
   Printing Office, Sept. 1970.

2. SMG Marketing Group, Inc.  Hospital Market Database.  Chicago: Healthcare
   Information Specialists.  1987.

3. SMG Marketing Group, Inc.  Hospital Market Database.  Chicago: Healthcare
   Information Specialists.  April 1991.

4. SMG Marketing Group, Inc.  Hospital Market Database.  Chicago: Healthcare
   Information Specialists.  April 1994.

5. Estimates from Two Survey Designs:  National Hospital Discharge Survey, by 
   B. Haupt and L. J. Kozak, Vital and Health Statistics.  DHHS Pub. No. (PHS) 
   92-1772, Series 13, No.111. Public Health Service. Washington. U. S. Government 
   Printing Office, May 1992.

6. Office of the Secretary,  Department of Health and Human Services:  Health
   Information Policy Council: 1984 Revision of the Uniform Hospital Discharge 
   Data Set.  Federal Register,Volume 50, No. 147. July 31, 1985.

7. National Center for Health Statistics:  International Classification of Diseases, 
   9th Revision, Clinical Modification.  DHHS Pub. No. (PHS) 80-1260.  Public Health 
   Service.  Washington. U.S. Government Printing Office, Sept. 1980.

8. Shah, B.V. 1981.  SESUDAAN:  Standard Errors Program for Computing of
   Standardized Rates from Sample Survey Data.  Research Triangle Institute. 
   Research Triangle Park, N.C.

9. Adjustment of Hospital Utilization Rates--United States, 1965-80, by R. Pokras 
   and L.J. Kozak.  Vital and Health Statistics.  DHHS Pub. No. (PHS) 85-1742, 
   Series 13, No.81.  Public Health Service. Washington. U. S. Government Printing 
   Office, Dec. 1984.

II.  TECHNICAL DESCRIPTION OF TAPE
  
  Data Set Name (Non-Newborns)----------------BG00.NHDS7996.NOT.NEWBORN
  Data Set Name (Newborns)------------------------BG00.NHDS7996.NEWBORN
  Number of Cartridges  (Non-Newborns)--------------------------------1
  Number of Cartridges  (Newborns)------------------------------------1
  Number of Recording Tracks ----------------------------------------18
  Density (bpi)-----------------------------------------------------38k
  Language-------------------------------------------------------EBCDIC
  Parity------------------------------------------------------------Odd 
  Record Length------------------------------------------------------83 
  Block Size-----------------------------------------------------31,200
  Number of Records (Non-Newborns)----------------------------3,778,368 
  Number of Records (Newborns)----------------------------------422,512

III.  TAPE RECORD FORMAT
 
  This section provides detailed information for each sampled record on the file, with a
  description of the coding of each item included on the record.  Data elements are arranged
  sequentially according to their physical location on the record.  Unless otherwise stated in
  the Item Description, the data are derived from the abstract form or from automated
  sources.  The SMG Hospital Market Tape and the hospital interview are alternate sources
  of data; some other items are computer generated.  NATIONAL HOSPITAL DISCHARGE SURVEY, Multi-year Data File

LAYOUT AND CODING OF DATA ITEMS

VARIABLE	POSITION	COMMENTS
Survey Year	1-2	2-digit value for each data year (i.e. 79 to 96). NOTE: Century designation is located in col. 81-82.
Newborn Flag	3	Flag for NEWBORN records: 1 = Newborn 2 = Non-Newborn
Units for Age	4	1 = Years 2 = Months 3 = Days
Age	5-6	If Units = Years: 00-99 If Units = Months: 01-11 If Units = Days: 00-31 NOTE: Ages 100 years and over were recoded to 99 years.
Sex	7	1 = Male 2 = Female
Race	8	1 = White 2 = Black 3 = American Indian/Eskimo 4 = Asian/Pacific Islander 5 = Other 9 = Race Not Stated NOTE: For 1979, only codes 1, 2, and 9 are available.
Marital Status	9	1 = Married 2 = Single 3 = Widowed 4 = Divorced 5 = Separated 6 = Unknown 9 = Not Stated
Month of Admission	10-11	01 = January . . . 12 = December 99 = Missing (1996 only)
Discharge Status	12	1 = Routine/Discharged Home 2 = Left Against Medical Advice 3 = Discharged/Transferred to Short Term Facility (In 1979 and 1980, D/T to Unspecified Facility) 4 = Discharged/Transferred to Long Term Facility (In 1979 and 1980, D/T to Organized Home Care) 5 = Alive, Disposition Not Stated (Option not coded in 1979 and 1980) 6 = Dead 9 = Disposition Not Stated
Days of Care	13-16	Use to calculate patient days of care; Values of zero generated by the computer from admission and discharge dates were changed to one. (Discharges for which dates of admission and discharge are the same are identified by the variable, Length of Stay Flag)
Length of Stay Flag	17	0 = Less than 1 day (admitted and discharged on the same day) 1 = 1 day or more
Geographic Region	18	1 = NorthEast 2 = MidWest 3 = South 4 = West
Number of Beds, Interview Recode	19	1 = 6-99 2 = 100-199 3 = 200-299 4 = 300-499 5 = 500 and over
Hospital Ownership	20	1 = Proprietary 2 = Government 3 = Not for Profit
Analysis Weight	21-25	Use to obtain weighted estimates
Principal Expected Source of Payment	26	0 = No Charge 1 = Worker’s Compensation 2 = Medicare 3 = Medicaid 4 = Other Government Payments 5 = Blue Cross 6 = Other Private/Commercial Ins. 7 = Self-Pay 8 = Other 9 = Payment Not Stated
Secondary Expected Source of Payment	27	Same coding as principal, above
Diagnosis Code #1	28-32	ICD-9-CM Diagnosis Code #1 *
Diagnosis Code #2	33-37	ICD-9-CM Diagnosis Code #2 *
Diagnosis Code #3	38-42	ICD-9-CM Diagnosis Code #3 *
Diagnosis Code #4	43-47	ICD-9-CM Diagnosis Code #4 *
Diagnosis Code #5	48-52	ICD-9-CM Diagnosis Code #5 *
Diagnosis Code #6	53-57	ICD-9-CM Diagnosis Code #6 *
Diagnosis Code #7	58-62	ICD-9-CM Diagnosis Code #7 *
Procedure Code #1	63-66	ICD-9-CM Procedure Code #1 *
Procedure Code #2	67-70	ICD-9-CM Procedure Code #2 *
Procedure Code #3	71-74	ICD-9-CM Procedure Code #3 *
Procedure Code #4	75-78	ICD-9-CM Procedure Code #4 *
Discharge Month	79-80	01 = January . . . 12 = December
First 2 digits of DataYear	81-82	19 = 1900's Starting in data year 2000, the value 20 will be assigned.
Partial/Full Responding Hospital	83	0 = Hospital responded for 12 months 1 = Hospital is partial respondent (i.e. Hospital responded for fewer than 12 months)

APPENDIX A

DEFINITION OF TERMS

  Terms Relating to Hospitals and Hospitalization

  HOSPITALS-Short-stay hospitals or hospitals whose specialty is general (medical or
  surgical), or children's general.  Hospitals must have 6 or more beds staffed for patient
  use.  Federal hospitals and hospital units of institutions are not included.

  TYPE OF OWNERSHIP OF HOSPITAL-The type of organization that controls and
  operates the hospital.  Hospitals are grouped as:     
            
  NOT FOR PROFIT - Hospitals operated by a church or another not for
  profit organization.     
  
  GOVERNMENT - Hospitals operated by State and local government.     
 
  PROPRIETARY - Hospitals operated by individuals, partnerships, or
  corporations for profit.

  PATIENT-A person who is formally admitted to the inpatient service of a short-stay
  hospital for observation, care, diagnosis, or treatment, or by birth.

  DISCHARGE-The formal release of a patient by a hospital; i.e. the termination of a
  period of hospitalization by death or by disposition to place of residence, nursing home,
  or another hospital.  The terms "discharges" and "patients discharged" are used
  synonymously.

  DISCHARGE RATE-The ratio of the number of hospital discharges during the year to
  the number of persons in the civilian population on July 1 of that year.

  DAYS OF CARE-The total number of patient days accumulated at time of discharge by
  patients discharged from short-stay hospitals during a year.  A stay of less than 1 day
  (patient admission and discharge on the same day) is counted as 1 day in the summation
  of total days of care.  For patients admitted and discharged on different days, the number
  of days of care is computed by counting all days from (and including) the date of
  admission to (but not including) the date of discharge.

  RATE OF DAYS OF CARE-The ratio of the number of patient days accumulated at time
  of discharge to the number of persons in the civilian population on July 1 of that year.

  AVERAGE LENGTH OF STAY-The total number of days of care accumulated at time
  of discharge by patients discharged during the year, divided by the number of patients
  discharged.

  Terms Relating to Diagnoses and Procedures

  DISCHARGE DIAGNOSES-One or more diseases or injuries (or some factor that
  influences health status and contact with health services that is not itself a current illness
  or injury) listed by the attending physician on the medical record of a patient.  In the
  NHDS, discharge (or final) diagnoses listed on the face sheet (summary sheet) of the
  medical record are transcribed in the order listed.  Each sample discharge is assigned a
  maximum of seven, five-digit codes according to ICD-9-CM (see Reference 5).

  PRINCIPAL DIAGNOSIS-The condition established after study to be chiefly responsible
  for occasioning the admission of the patient to the hospital for care.

  FIRST-LISTED DIAGNOSIS-The coded diagnosis identified as the principal diagnosis
  or listed first on the face sheet of the medical record if the principal diagnosis cannot be
  identified. The number of first-listed diagnoses is equivalent to the number of discharges.

  PROCEDURE-One or more surgical or nonsurgical operations, procedures, or special
  treatments listed by the physician on the medical record.  In the NHDS, all terms listed on
  the face sheet (summary sheet) of the medical record under the caption "operation",
  "operative procedures", "operations and/or special treatment", and the like are transcribed
  in the order listed.  A maximum of four procedures are coded.     Historically, procedures
  were categorized into four classes according to UHDDS guidelines.  Classes 1-3
  consisted of significant procedures, i.e., those that carried an operative or anesthetic risk
  or required highly trained personnel, special facilities, or special equipment.  Class 4
  procedures were not considered significant; therefore, reporting was optional.  From 1979
  through the middle of 1983, only three Class 4  procedures were coded for the NHDS: 
  circumcision, episiotomy, and removal of intrauterine contraceptive device.  Since the
  last half of 1983, additional codes were added, until 1991, when all procedures were
  coded.

  RATE OF PROCEDURES-The ratio of the number of all-listed procedures during a year
  to the number of persons in the civilian population on July 1 of that year.

  Demographic Terms

  AGE-Refers to the age of the patient on the birthday prior to admission to the hospital
  inpatient service.

  POPULATION-Civilian population is the resident population excluding members of the
  Armed Forces.

  GEOGRAPHIC REGION-Hospitals are classified by location in one of the four
  geographic regions of the United States corresponding to those used by the U.S. Bureau
  of the Census:

  NORTHEAST       MIDWEST        SOUTH                 WEST
  Maine           Michigan       Delaware              Montana
  New Hampshire   Ohio           Maryland              Idaho
  Vermont         Illinois       District of Columbia  Wyoming
  Massachusetts   Indiana        Virginia              Colorado
  Rhode Island    Wisconsin      West Virginia         New Mexico
  Connecticut     Minnesota      North Carolina        Arizona
  New York        Iowa           South Carolina        Utah
  New Jersey      Missouri       Georgia               Nevada
  Pennsylvania    North Dakota   Florida               Washington
                  South Dakota   Kentucky              Oregon
                  Nebraska       Tennessee             California
                  Kansas         Alabama               Hawaii
                                 Mississippi           Alaska
                                 Arkansas
                                 Louisiana
                                 Oklahoma
                                 Texas

APPENDIX B

  The International Classification of Diseases, 9th Revision, Clinical Modification has
  been used for coding medical data in the NHDS since 1979.  However, since 1986, the
  classification system has undergone annual updating.  The changes, which include
  assignment of new diagnostic and procedure codes, fourth and fifth digit expansion of
  codes, as well as code deletions, have been released for the years 1986 through 1996. 
  These changes are published in an Addendum and become effective October 1 of the
  calendar year. Addenda are developed by the ICD-9-CM Coordination and Maintenance
  Committee and approved by the Director of NCHS and the Administrator of the Health
  Care Financing Administration.

  It is important to recognize that, for the year in which a code undergoes revision,
  estimates for both the original and the revised code are not accurate, since each code was
  used for only part of the year.  Therefore, for codes which are revised in a given year, it is
  advisable to use data for the year following the revision to produce an estimate. However,
  for the 1992 through 1996 data years, any codes assigned which were consistent with the
  October Addendum of that year were changed back to their previous codes in order to
  avoid the problem of partial year estimates being mistaken for full year estimates.

  In order to assist users in data retrieval, a conversion table is provided that shows for each
  new code, its date of introduction and the previously assigned code equivalent, which had
  been used for reporting the selected diagnosis or procedure prior to issuance of the new
  code.   This table shows coding changes up to October 1995.

DIAGNOSIS CODES

DIAGNOSIS CODES

	Effective
Current code(s) assignment	October 1	Previous code(s) assignment

005.81	1995	005.8
005.89	1995	005.8

008.00-008.09	1992	008.0
008.43-008.47	1992	008.49
008.61-008.69	1992	008.6

041.00-041.09	1992	041.0
041.10-041.19	1992	041.1
041.81-041.89	1992	041.8

041.86	1995	041.84

042	1994	042.0-042.2,042.9,043.0-043.3,
		043.9,044.0,044.9

042.0-042.9	1986	279.19
043.0-043.9	1986	279.19
044.0-044.9	1986	279.19

070.20-070.21	1991	070.2

070.22	1994	070.20
070.23	1994	070.21

070.30-070.31	1991	070.3

070.32	1994	070.30
070.33	1994	070.31

070.41-070.49	1991	070.4

070.44	1994	070.41

070.51-070.59	1991	070.5

070.54	1994	070.51

077.98-077.99	1993	077.9

078.10-078.11,078.19	1993	078.1

078.88	1993	078.89

079.4	1993	079.8
079.50-079.53,079.59	1993	079.8

079.81	1995	079.89

079.88-079.89	1993	079.8

079.98-079.99	1993	079.9

088.81,088.89	1989	088.8

088.82	1993	088.89

099.40-099.49	1992	099.4
099.50-099.59	1992	078.89

112.84-112.85	1992	112.89

114.4-114.5	1993	114.3

176.0-176.9	1991	173.0-173.9

203.00	1991	203.0
203.01	1991	V10.79
203.10	1991	203.1
203.11	1991	V10.79
203.80	1991	203.8
203.81	1991	V10.79

204.00	1991	204.0
204.01	1991	V10.61
204.10	1991	204.1
204.11	1991	V10.61
204.20	1991	204.2
204.21	1991	V10.61
204.80	1991	204.8
204.81	1991	V10.61
204.90	1991	204.9
204.91	1991	V10.61

205.00	1991	205.0
205.01	1991	V10.62
205.10	1991	205.1
205.11	1991	V10.62
205.20	1991	205.2
205.21	1991	V10.62
205.30	1991	205.3
205.31	1991	V10.62
205.80	1991	205.8
205.81	1991	V10.62
205.90	1991	205.9
205.91	1991	V10.62

206.00	1991	206.0
206.01	1991	V10.63
206.10	1991	206.1
206.11	1991	V10.63
206.20	1991	206.2
206.21	1991	V10.63
206.80	1991	206.8
206.81	1991	V10.63
206.90	1991	206.9
206.91	1991	V10.63

207.00	1991	207.0
207.01	1991	V10.69
207.10	1991	207.1
207.11	1991	V10.69
207.20	1991	207.2
207.21	1991	V10.69
207.80	1991	207.8
207.81	1991	V10.69

208.00	1991	208.0
208.01	1991	V10.60
208.10	1991	208.1
208.11	1991	V10.60
208.20	1991	208.2
208.21	1991	V10.60
208.80	1991	208.8
208.81	1991	V10.60
208.90	1991	208.9
208.91	1991	V10.60

237.70-237.72	1990	237.7

250.02	1993	250.90
250.03	1993	250.91
250.12	1993	250.10
250.13	1993	250.11
250.22	1993	250.20
250.23	1993	250.21
250.32	1993	250.30
250.33	1993	250.31
250.42	1993	250.40
250.43	1993	250.41
250.52	1993	250.50
250.53	1993	250.51
250.62	1993	250.60
250.63	1993	250.61
250.72	1993	250.70
250.73	1993	250.71
250.82	1993	250.80
250.83	1993	250.81
250.92	1993	250.90
250.93	1993	250.91

278.00-278.01	1995	278.0

283.10-283.11,283.19	1993	283.1

305.1	1994	305.10,305.11,305.12,
		305.13 (delete code)

312.81-312.82,381.89	1994	312.8

320.81-320.89	1992	320.8

333.92-333.93	1994	333.99

337.20-337.22,337.29	1993	337.9

342.00-342.02	1994	342.0
342.10-342.12	1994	342.1
342.80-342.82	1994	342.9
342.90-342.92	1994	342.9

344.00-344.04,344.09	1994	344.0
344.30-344.32	1994	344.3
344.40-344.42	1994	344.4

344.81,344.89	1993	344.8

345.00-345.01	1989	345.0
345.10-345.11	1989	345.1
345.40-345.41	1989	345.4
345.50-345.51	1989	345.5
345.60-345.61	1989	345.6
345.70-345.71	1989	345.7
345.80-345.81	1989	345.8
345.90-345.91	1989	345.9

346.00-346.01	1992	346.0
346.10-346.11	1992	346.1
346.20-346.21	1992	346.2
346.80-346.81	1992	346.8
346.90-346.91	1992	346.9

355.71	1993	354.4
355.79	1993	355.7

371.82	1992	371.89

374.87	1990	374.89

403.00-403.01	1989	403.0
403.10-403.11	1989	403.1
403.90-403.91	1989	403.9

404.00-404.03	1989	404.0
404.10-404.13	1989	404.1
404.90-404.93	1989	404.9

410.00-410.02	1989	410.0
410.10-410.12	1989	410.1
410.20-410.22	1989	410.2
410.30-410.32	1989	410.3
410.40-410.42	1989	410.4
410.50-410.52	1989	410.5
410.60-410.62	1989	410.6
410.70-410.72	1989	410.7
410.80-410.82	1989	410.8
410.90-410.92	1989	410.9

411.81	1989	410.9
411.89	1989	411.8

414.00-414.01	1994	414.0
414.02-414.03	1994	996.03

415.11	1995	997.3 & 415.1
415.19	1995	415.1

429.71	1989	410.0-410.9
429.79	1989	410.0-410.9

433.00-433.01	1993	433.0
433.10-433.11	1993	433.1
433.20-433.21	1993	433.2
433.30-433.31	1993	433.3
433.80-433.81	1993	433.8
433.90-433.91	1993	433.9

434.00-434.01	1993	434.0
434.10-434.11	1993	434.1
434.90-434.91	1993	434.9

435.3	1995	435.0 & 435.1

437.7	1992	780.9

440.20-440.22	1992	440.2

440.23	1993	440.20 & 707.1 or 707.8 or 707.9
440.24	1993	440.20 & 785.4
440.29	1993	440.20

440.30-440.32	1994	996.1

441.00-441.03	1994	441.0

441.6	1993	441.1 & 441.3
441.7	1993	441.2 & 441.4

446.20-446.21,446.29	1990	446.2

451.82-451.84	1993	451.89

458.2	1995	997.9 & 458.9

482.30-482.39	1992	482.3
482.81-482.89	1992	482.8

483.0	1992	483
483.8	1992	483

491.20-491.21	1991	491.2

493.20	1989	493.90
493.21	1989	493.91

512.1	1994	997.3

518.81	1987	799.1
518.82-518.89	1987	518.8

524.00-524.09	1992	524.0
524.10-524.19	1992	524.1
524.60-524.69	1991	524.6
524.70-524.79	1992	524.8

530.10-530.11, 530.19	1993	530.1
530.81	1993	530.1
530.82-530.84, 530.89	1993	530.8

535.00-535.01	1991	535.0
535.10-535.11	1991	535.1
535.20-535.21	1991	535.2
535.30-535.31	1991	535.3
535.40-535.41	1991	535.4
535.50-535.51	1991	535.5
535.60-535.61	1991	535.6

536.3	1994	536.8

537.82	1990	537.89
537.83	1991	537.82

556.0-556.6	1994	556
556.8-556.9	1994	556

562.02	1991	562.00
562.03	1991	562.01
562.12	1991	562.10
562.13	1991	562.11

569.60-569.61	1995	569.6
569.69	1995	569.6

569.84	1990	557.1
569.85	1991	569.84

593.70-593.73	1994	593.7

596.51-596.53	1992	596.5
596.54	1992	344.61
596.55-596.59	1992	596.5

599.81-599.89	1992	599.8

645.0	1991	645

651.30-651.31,651.33	1989	651.00-651.01,651.03
651.40-651.41,651.43	1989	651.10-651.11,651.13
651.50-651.51,651.53	1989	651.20-651.21,651.23
651.60-651.61,651.63	1989	651.80-651.81,651.83

654.20-654.21,654.23	1990	654.2,654.9
654.90-651.94	1990	654.2,654.9

657.0	1991	657

659.60,659.61,659.63	1992	659.80,659.81,659.83

665.10,665.11	1992	665.10,665.11,665.12,665.14

Note: The title for the subcategory, 665.1 has been changed,
making the fifth-digit subclassification, 665.12 and 665.14
invalid.

670.0	1991	670

672.0	1991	672

677	1994	* No previous code assignments.

690.10	1995	690
690.11	1995	691.8 & 704.8
690.12	1995	691.8
690.18	1995	690
690.8	1995	690

692.72-692.74	1992	692.79
692.82-692.83	1992	692.89

702.0-702.8	1991	702

702.11,702.19	1994	702.1

704.02	1993	704.09

709.00-709.01,709.09	1994	709.0

710.5	1992	288.3,729.1

728.86	1995	729.4

733.10-733.16, 733.19	1993	733.1

738.10-738.19	1992	738.1

747.60-747.64, 747.69	1993	747.6
747.82	1993	747.89

753.10-753.17,753.19	1990	753.1

759.81-759.89	1989	759.8

759.83	1994	759.89

760.75	1991	760.79

760.76	1994	760.79

764.00-764.09	1988	764.0
764.10-764.19	1988	764.1
764.20-764.29	1988	764.2
764.90-764.99	1988	764.9

765.00-765.09	1988	765.0
765.10-765.19	1988	765.1

780.01-780.09	1992	780.0

780.03	1993	780.01

780.57	1992	780.51,780.53

781.8	1994	781.9

787.01-787.03	1994	787.0

787.91	1995	558.9
787.99	1995	787.9

788.20-788.21, 788.29	1993	788.2
788.30-788.39	1992	788.3
788.41-788.43	1993	788.4
788.61-788.62, 788.69	1993	788.6

789.00-789.07, 789.09	1994	789.0
789.30-789.37, 789.39	1994	789.3
789.40-789.47, 789.49	1994	789.4
789.60-789.67, 789.69	1994	789.6

790.91	1993	790.9
790.92	1993	286.9
790.93, 790.99	1993	790.9

795.71	1994	795.8 (delete code)
795.79	1994	795.7

795.8	1986	795.7

864.05	1992	864.09
864.15	1992	864.19

909.5	1994	909.9

925.1-925.2	1993	925

989.81-989.84	1995	989.8
989.89	1995	989.8

995.60-995.69	1993	995.0

996.04	1994	996.09

996.51-996.59	1987	996.5
996.60-996.69	1989	996.6
996.70-996.79	1989	996.7
996.80-996.89	1987	996.8

996.85	1990	999.8

997.00-997.01	1995	997.0
997.02	1995	997.9 & 430-434, 436
997.09	1995	997.0
997.91	1995	997.9
997.99	1995	997.9

998.81-998.82, 998.89	1994	998.8

V03.81-V03.82, V03.89	1994	V03.8

V05.3-V05.4	1993	V05.8

V06.5-V06.6	1994	V06.8

V07.31,V07.39	1994	V07.3

V07.4	1992	V07.8

V08	1994	044.9, 795.8 (delete code)

V09.0-V09.91	1993	* No previous code assignments

V12.00-V12.03, V12.09	1994	V12.0

V12.50-V12.52	1995	V12.5
V12.59	1995	V12.5

V12.70-V12.72, V12.79	1994	V12.7

V13.00-V13.01, V13.09	1994	V13.0

V15.82	1994	305.13 (delete code)

V15.84-V15.86	1995	V15.89

V25.43	1992	V25.49
V25.5	1992	V25.8

V29.0-V29.8	1992	V71.8
V29.9	1992	V71.9

V30.00-V30.01	1989	V30.0
V31.00-V31.01	1989	V31.0
V32.00-V32.01	1989	V32.0
V33.00-V33.01	1989	V33.0
V34.00-V34.01	1989	V34.0
V35.00-V35.01	1989	V35.0
V36.00-V36.01	1989	V36.0
V37.00-V37.01	1989	V37.0
V39.00-V39.0l	1989	V39.0

V43.60-V43.66, V43.69	1994	V43.6

V43.81-V43.82	1995	V43.8
V43.89	1995	V43.8

V45.00	1994	V45.89
V45.01	1994	V45.0
V45.02, V45.09	1994	V45.89

V45.51	1994	V45.5
V45.52, V45.59	1994	V45.89
V45.82	1994	V45.89

V45.83	1995	V45.89

V49.60-V49.67	1994	V49.5
V49.70-V49.77	1994	V49.5

V50.41-V50.42, V50.49	1994	V50.8

V53.31	1994	V53.3
V53.32, V53.39	1994	V53.9

V56.1	1995	V58.89

V57.21-V57.22	1994	V57.2

V58.41, V58.49	1994	V58.4

V58.61	1995	V67.51
V58.69	1995	V67.51

V58.81, V58.89	1994	V58.8

V58.82	1995	V58.89

V59.01-V59.02	1995	V59.0
V59.09	1995	V59.0
V59.6	1995	V59.8

V65.40-V65.45, V65.49	1994	V65.4

V69.0-V69.3	1994	* No previous code assignments.
V69.8-V69.9	1994	* No previous code assignments.

V72.81-V72.85	1993	V72.8
V73.88-V73.89	1993	V73.8
V73.98-V73.99	1993	V73.9

E854.8	1995	E858.8

E869.4	1994	E869.8

E880.1	1995	E884.9
E884.3-E884.4	1995	E884.2
E884.5-E884.6	1995	E884.9

E906.5	1995	E906.3
E908.0-E908.4	1995	E908
E908.8-E908.9	1995	E908
E909.0-E909.4	1995	E909
E909.8-E909.9	1995	E909
E920.5	1995	E920.4
E924.2	1995	E924.0
E968.5	1995	E968.8

  
PROCEDURE CODES

PROCEDURE CODES

	Effective
Current code(s) assignment	October 1	Previous code(s) assignment

2.96	1992	89.19
3.9	1987	03.99 (Insertion of Catheter)

5.25	1995	39.7 (delete)

11.75	1989	11.79
11.76	1989	11.62

20.96-20.98	1986	20.95

22.12	1988	22.11

26.12	1988	26.11

29.31	1991	83.02
29.32	1991	29.3
29.33	1991	29.3
29.39	1991	29.3

31.45	1988	31.43-31.44

31.95	1989	31.75

32.01	1989	32
32.09	1989	32

32.22	1995	32.29, 32.9

32.28	1989	32.29

33.27	1987	33.22 + 33.27
33.28	1987	33.27
33.29	1987	33.28-33.29

33.5	1995	33.5
33.51	1995	33.5
33.52	1995	33.5

33.6	1990	33.5 + 37.5

34.05	1994	34.99

35.84	1988	35.82
35.96	1986	35.03

36.00-36.03	1986	36
36.04	1986	39.97
36.05	1987	36.01
36.05	1986	36.01 (Before October 1986 contents of current code 36.05 would have been assigned to 36.0), 36.02
36.06	1995	36.01, 36.02, 36.03, 36.05

36.09	1986	36
36.09	1991	36.00 (Code Deleted)

37.26-37.27	1988	37.29
37.34	1988	37.33

37.65	1995	37.62
37.66	1995	37.62

37.70 (Leads only)	1987	37.70 (Leads/Device)
37.71-37.72 (Leads only)	1987	37.74 (Leads/Device)
37.73 (Leads only)	1987	37.73 (Leads/Device)
37.74 (Leads only)	1987	37.76 (Leads/Device)
37.75 (Leads only)	1987	37.89 (Leads/Device)
37.76 (Leads only)	1987	37.81 (Leads/Device)
37.77 (Leads only)	1987	37.83-37.84 (Leads/Device)
37.78	1987	37.71-37.72
37.79	1987	86.09

37.80-37.87	1992	89.49 (Code deleted, this procedure is included in the code for pacemaker insertion/replacement)

37.80 (Device only)	1987	37.73-37.77 (Leads/Device)
37.81 (Device only)	1987	37.73-37.77 (Leads/Device)
37.82 (Device only)	1987	37.73-37.77 (Leads/Device)
37.83 (Device only)	1987	37.73-37.77 (Leads/Device)
37.85-37.87	1987	37.85
37.89	1987	37.86 + 37.89
37.94-37.98	1986	37.99

38.22	1986	38.29

38.44 (Abdominal Aorta Only)	1986	38.44 (Entire Aorta)
38.45 (Thoracic Aorta Added)	1986	38.44-38.45
38.95	1989	38.93

39.28	1991	39.29

39.5	1995	39.59

39.65	1988	39.61
39.66	1990	39.65

41.00-41.03	1988	41

41.04	1994	99.79

42.25	1988	42.24
42.33	1989	42.32, 42.39
42.33	1990	42.91

43.11	1989	43.1
43.19	1989	43.1, 43.2
43.41	1989	43.41,43.49

44.21	1986	44.2
44.22	1986	44.99
44.29	1986	44.2
44.43	1989	43.49,45.32
44.44	1989	38.86
44.49	1989	43
44.93-44.94	1986	44.99

45.16	1988	45.14 (45.15 before 1987)
45.3	1989	45.31,45.32
45.42	1988	45.41
45.43	1989	45.49
45.75 (Hartmann Resection Added)	1988	48.66 (Code Deleted)
45.95	1987	45.93

46.13	1992	46.12 (Code Deleted)
46.32	1989	46.39
46.85	1989	46.99

48.36	1995	45.42

49.31	1989	49.3
49.39	1989	49.3

51.1	1989	51.97
51.11	1989	51.11,51.97
51.14	1989	51.12
51.15	1989	51.97
51.22	1991	51.21 (Code Deleted),51.22
51.23	1991	51.22
51.64	1989	51.69
51.84-51.88	1989	51.97

51.97	1986	52.91,51.99, or 51.82
51.98	1986	51.99

52.13	1989	51.97,52.91
52.14	1989	52.11
52.21	1989	52.2
52.22	1989	52.2
52.93	1989	52.93 + 52.91
52.94	1989	52.09
52.97	1989	52.91
52.98	1989	52.91
52.99	1989	52.93,52.94,52.99

54.24	1987	54.23

54.25	1993	54.98

55.03-55.04	1986	55.02

56.33-56.34	1987	56.33
56.35	1987	45.12

57.17-57.18	1989	57.21
57.22	1989	57.22,57.82

58.31	1990	58.3
58.39	1990	58.3
58.93	1986	57.99

59.72	1995	59.79

59.96	1986	59.95

60.21	1995	60.2
60.29	1995	60.2

60.95	1991	60.99

64.97	1986	64.95

66.01	1992	66
66.02	1992	66.73

68.15	1987	68.14
68.16	1987	68.13
68.9	1992	68.4

74.3	1992	69.11 (Code Deleted)

77.56	1989	77.89,78.49,81.18
77.57	1989	77.89,80.48,81.18,83.85
77.58	1989	77.59,81.18

78.1	1991	78.4
78.11	1991	78.41
78.12	1991	78.42
78.13	1991	78.43
78.14	1991	78.44
78.15	1991	78.45
78.16	1991	78.46
78.17	1991	78.47
78.18	1991	78.48
78.19	1991	78.49
78.2	1991	78.10,78.20,78.30
78.21	1991	78.11,78.31
78.22	1991	78.12,78.22,78.32
78.23	1991	78.13,78.23,78.33
78.24	1991	78.14,78.34
78.25	1991	78.15,78.25,78.35
78.27	1991	78.17,78.27,78.37
78.28	1991	78.18,78.38
78.29	1991	78.11,78.16,78.19,78.29,78.39
78.39	1991	78.31

78.90 (1)	1987	78.4
78.91 (1)	1987	78.41
78.92 (1)	1987	78.42
78.93 (1)	1987	78.43
78.94 (1)	1987	78.44
78.95 (1)	1987	78.45
78.96 (1)	1987	78.46
78.97 (1)	1987	78.47
78.98 (1)	1987	78.48
78.99 (1)	1987	78.49

80.50-80.59	1986	80.5

81.03	1989	81.02
81.04-81.05	1989	81.03,81.04,81.05
81.06-81.07	1989	81.06,81.07
81.08	1989	81.06,81.07,81.08
81.09	1989	81.08
81.4	1989	81.69
81.51	1989	81.51,81.59
81.52	1989	81.61,81.62,81.63,81.64
81.53	1989	81.51,81.59,81.61,81.62,
		81.63,81.64
81.54-81.55	1989	81.41
81.56	1989	81.48
81.57	1989	81.31,81.39
81.59	1989	81.39
81.72	1989	81.79
81.73-81.74	1989	81.86
81.75	1989	81.87
81.79	1989	81.79,81.87
81.8	1989	81.81
81.97	1992	81.59

85.95	1987	85.99
85.96	1987	85.99

86.06	1987	86.09
86.07	1990	86.09
86.27	1986	86.22-86.23
86.28	1988	86.22
86.93	1987	86.89

88.9	1986	88.39
88.91	1986	89.15
88.92	1986	89.39
88.93	1986	89.15
88.94	1986	89.39
88.95	1986	89.29
88.97	1989	88.99
88.98	1989	88.9
88.99	1986	89.39

89.1	1989	89.15
89.17-89.18	1988	89.15
89.19	1989	89.15
89.5	1991	89.54

92.3	1995	01.59, 04.07, 07.63, 07.68

93.9	1988	93.92

94.61-94.69	1989	94.25

96.6	1986	96.35
96.7	1991	93.92 (Code Deleted)
96.71	1991	93.92 (Code Deleted)
96.72	1991	93.92 (Code Deleted)

97.05	1989	51.97

98.51-98.52	1989	59.96 (Code Deleted)
98.59	1989	59.96 (Code Deleted)

99	1995	99.02

99.15	1986	99.29

99.28	1994	99.25

99.71-99.79 (2)	1988	99.07
99.85	1987	93.35
99.86	1987	93.39
99.88	1988	99.83

(1) Codes 78.90-78.99 were retitled as "Insertion of bone growth
stimulator" in October 1987; the previous contents of codes
78.90-78.99 were reassigned to codes 78.40-78.49.

(2) Codes 99.71-99.79 were deleted in October 1987; their contents
were not transferred elsewhere. In the October 1988 revision,
codes 99.71-99.79 were reclassified as "Therapeutic apheresis."

  
APPENDIX C

  Historically, operative and surgical procedures were categorized into four classes,
  according to UHDDS guidelines.  Classes 1-3 consisted of significant procedures, i.e.
  those that carried an operative or anesthetic risk or required highly trained personnel,
  special facilities, or special equipment.  Class 4 procedures were not considered
  significant; therefore, reporting was optional.  From 1979 through the middle of 1983,
  only three Class 4 procedures were coded for the NHDS: circumcision, episiotomy, and
  removal of intrauterine contraceptive device.  Since the last half of 1983, additional codes
  were added, until 1991, when all procedures were coded.

  It is important to remember that, because many procedure codes were not utilized
  between 1979 and 1990, it is not possible to produce estimates for those codes.  The table
  contained in this appendix lists the procedures not coded and the year the code was first
  used.   Caution should be exercised when producing estimates for these codes.

CLASS 4 PROCEDURES AND YEAR CODE FIRST USED IN NHDS
ICD-9-CM	First	ICD-9-CM	First	ICD-9-CM	First	ICD-9-CM	First
Procedure Code	used	Procedure Code	used	Procedure Code	used	Procedure Code	used
01.18-01.19	1983	38.29	1983	71.19	1983	89.66	1989
03.39	1983	40.19	1983	73.6-	1979	89.7-	1991
04.19	1983	41.38-41.39	1989	73.91-73.92	1989	90.01-91.99	1991
05.19	1983	42.29	1989	75.35	1989	93.01-93.25	1991
06.19	1983	44.91	1989	76.19	1983	93.27-93.28	1991
07.19	1983	45.19	1989	78.80-78.89	1983	93.31-93.39	1991
08.19	1989	45.28-45.29	1989	81.98	1983	93.42-93.44	1989
08.91-08.93	1983	48.23	1989	83.29	1983	93.61-93.89	1991
09.19	1983	48.29	1989	85.19	1989	93.91	1991
09.41-09.49	1983	49.21	1989	86.19	1989	93.94	1989
10.29	1983	49.29	1989	86.92	1989	93.96	1989
11.29	1983	49.41	1989	87.09-87.12	1991	93.99	1989
12.29	1983	50.19	1983	87.16-87.17	1991	94.01-94.23	1991
14.19	1983	51.19	1983	87.22-87.29	1991	94.25	1991
15.09	1983	52.19	1983	87.36-87.37	1989	94.29-94.59	1991
16.21	1989	54.29	1983	87.39	1991	95.01-95.03	1991
16.29	1983	55.29	1983	87.43-87.49	1991	95.05-95.11	1991
18.01	1989	56.39	1983	87.69	1989	95.14-95.15	1991
18.11	1989	57.39	1983	87.79	1989	95.31-95.48	1991
18.19	1989	58.29	1989	87.85-87.89	1991	95.49	1989
20.39	1983	59.29	1983	87.92	1991	96.09	1989
21.21	1989	60.18	1983	87.95-87.99	1991	96.11-96.19	1991
21.29	1989	61.19	1989	88.09	1991	96.26-96.28	1991
22.19	1989	62.19	1983	88.16-88.31	1991	96.34-96.59	1991
24.19	1989	63.09	1983	88.33	1991	97.01-97.04	1991
25.09	1989	64.0-	1979	88.35	1991	97.14-97.69	1991
25.91	1989	64.19	1989	88.37	1991	97.71	1979
26.19	1989	64.91	1989	88.39	1991	97.72-97.89	1991
27.29	1989	64.94	1989	89.01-89.09	1991	99.02-99.14	1991
27.91	1989	65.19	1983	89.11-89.13	1991	99.16-99.24	1991
28.19	1983	66.19	1983	89.15-89.16	1991	99.26-99.59	1991
29.19	1989	67.19	1983	89.26-89.31	1991	99.71-99.79	1989
31.48-31.49	1989	68.19	1983	89.33-89.39	1991	99.82-99.84	1990
33.28-33.29	1983	69.92	1989	89.45-89.49	1989	99.91-99.99	1990
34.28-34.29	1983	70.21	1989	89.51-89.53	1989
37.29	1989	70.29	1983	89.55-89.59	1989

APPENDIX D

  The standard error is primarily a measure of sampling variability that occurs by chance
  because only a sample rather than the entire universe is surveyed.  The relative standard
  error of an estimate is obtained by dividing the standard error by the estimate itself. 
  When the resulting value is multiplied by 100, the relative standard error is expressed as a
  percent of the estimate.

  Before 1988, standard error estimates were produced using a computerized routine based
  on a rigorously unbiased algebraic estimator of the variance.  Since 1988, estimates of
  sampling variability have been calculated with SESUDAAN or SUDAAN software,
  which computes standard errors by using a first-order Taylor series approximation of the
  deviation of estimates from their expected values.  A description of the software and the
  approach it uses was published by Shah (see Reference 8).  Neither of these methods is
  available to analysts outside the NCHS/CDC research community.

  In order to obtain standard errors that would be applicable for a wide variety of statistics
  and that could be prepared at a moderate cost, a method using generalized variance curves
  was developed.  Numerous variances were calculated and a best fit formula was derived
  which was based on an empirically determined relationship between the size of an
  estimate, X, and its relative variance. The relative standard error was then obtained by
  taking the square root of the relative variance. These generalized variance curves
  provided approximations to the relative standard errors that were applicable to estimates
  of discharges, first- or all-listed diagnoses, all-listed procedures, and days of care, either
  aggregated or disaggregated by selected patient or hospital characteristics.

  This appendix contains information needed to produce generalized errors for NHDS
  statistics.  For the years 1979 through 1987, curves are represented in tables containing
  selected estimates of different sizes and their approximate relative standard errors. For the
  years 1988 through the present, tables containing parameter values for relative standard
  error curves are given.  Instructions on how to use this information follows. The RSE
  tables and curves for each data year are contained in separate files which are available on
  a computer disk provided with this documentation.

  COMPUTATION OF RELATIVE STANDARD ERRORS FOR AGGREGATE
  ESTIMATES, 1979 THROUGH 1987 DATA YEARS

  For each of the years from 1979 through 1987, there are files containing approximate
  relative standard errors (RSEs) for estimates of various sizes for discharges, first- or
  all-listed diagnoses, all-listed procedures, and days of care.  Because RSEs may differ
  depending on the characteristic which is being estimated, more than one RSE curve is
  usually presented.  Also, since it is not possible to provide exact standard errors for every
  size estimate, it is necessary to use arithmetic interpolation to obtain the RSE for an
  estimate not included in the table.  Linear interpolation is used for simplicity and without
  loss of accuracy, even though the curves are not strictly speaking linear functions.

  For example, in 1979 the estimated number of appendectomies (ICD-9-CM code 47.0)
  performed on patients 15 years and older discharged from short-stay hospitals was
  232,000.  Referring to the file, RSE79.WK1, there is no curve by age, so the one entitled
  "All Other Variables" is used. Also, the estimate 232,000 is not listed, so in order to
  obtain an approximate RSE, arithmetic interpolation is performed as follows.

  Step 1.  In the column headed "Size of Estimate", locate the two adjacent values between
  which the estimate of interest is located.  In this example, they would be 100,000 and
  250,000.

  Step 2.  For these estimates, compute estimated standard errors, using the corresponding
  RSEs from the column headed "All Other Variables".

       SE(100,000) = 9.9% * 100,000 = 9,900 
       SE(250,000) = 8.6% * 250,000 = 21,500

  Step 3.  Calculate the proportional part of the interval between 100,000 and 250,000
  which falls between 100,000 and 232,000.

       P = (232,000 - 100,000) / (250,000 - 100,000)  = .88

  Step 4.  Calculate the estimated standard error of 232,000 by subtracting the proportional
  part of the interval between the two standard errors from the standard error of 100,000.      
       SE(232,000) = SE(100,000) - P * (SE(100,000) - SE(250,000))
       SE(232,000) = 9,900 - .88 * (9,900 - 21,500) = 20,108

  The relative standard error can be obtained by dividing the standard error by the estimate:

       RSE(232,000) =  20,108 / 232,000 = .087

  When multiplied by 100, the RSE is expressed as a percent of the estimate (i.e. 8.7%).

  The standard error can be employed to generate confidence intervals for statistical testing. 
  In this example, the two-tailed, 95% confidence interval for the estimate of
  appendectomies for inpatients aged 15 and older in 1979 is:

       LOWER LIMIT:    232,000 - 1.96 * 20,108 = 192,588
       UPPER LIMIT:    232,000 + 1.96 * 20,108 = 271,412

  COMPUTATION OF RELATIVE STANDARD ERRORS FOR PERCENTS, 1979
  THROUGH 1987 DATA YEARS

  The relative standard error of a percent in which both the numerator (X) and denominator
  (Y) are from NHDS is estimated by:

       RSE(X/Y) = SQRT {[SE(X)^2 / X^2] - [SE(Y)^2 / Y^2]}

  To verbally clarify this formula, the RSE(X/Y) is obtained by taking the square root of
  the difference between two quantities.  The first of the two quantities is obtained by
  dividing the squared standard error of X by X-squared; the second of the two quantities is
  obtained by dividing the squared standard error of Y by Y-squared.  When RSE(X/Y) is
  multiplied by 100, then RSE(X/Y) is expressed as a percent of the estimate.

  For example, the estimated 232,000 appendectomies performed on patients aged 15 years
  and older represent 74.6% of the estimated 311,000 appendectomies in 1979.  To
  compute the relative standard error of this percent, the standard errors of both the
  numerator and the denominator are needed.  The standard error of the numerator is given
  above.  The standard error of the denominator can be calculated using the procedure
  described in the preceding section and is found to be 25,770.  Using these figures in the
  formula gives:

       RSE(.746) = SQRT [(20,108^2 / 232,000^2) - (25,770^2 / 311,000^2)]  = .025

  Expressed as a percent, RSE(.746) = 2.5%.

  The standard error of the percent can be obtained by multiplying the percent by its RSE:

       SE(.746) =  RSE(.746) * .746 = .025 * .746 = .019

  The standard error can be employed to generate confidence intervals around the estimate,
  as shown above.

  COMPUTATION OF RELATIVE STANDARD ERRORS FOR AGGREGATE
  ESTIMATES,  1988 THROUGH 1996 DATA YEARS

  The relative standard error of an estimate, RSE(X), may be calculated from the formula:

       RSE(X) = SQRT( a + b/X)

  with a and b provided in the accompanying files.  When multiplied by 100, RSE(X) is
  expressed as a percent of X.

  For example, in 1992 the estimated number of discharges from short-stay hospitals for
  females with a first-listed diagnosis of atherosclerotic heart disease (ICD-9-CM code
  414.0) was 130,000. Using the file, RSE92.WK1, in Appendix D for estimates by sex, the
  value of a is .00089 and the value for b is 404.530.  Thus,

       RSE(130,000) = SQRT [.00089 + (404.530 / 130,000)]  = .0633

  Expressed as a percent, RSE(130,000) = 6.33%.

  The standard error of the estimate is obtained by multiplying the relative standard error by
  the estimate itself:

       SE(130,000) =  130,000 * .0633  =  8,229

  The standard error can be employed to generate confidence intervals for statistical testing. 
  In this example, the two-tailed, 95% confidence interval for the estimate of female
  inpatients with a first-listed diagnosis of atherosclerotic heart disease in 1992 is:

       LOWER LIMIT:   130,000 - 1.96 * 8,229 = 113,871
       UPPER LIMIT:     130,000 + 1.96 * 8,229 = 146,129

  COMPUTATION OF RELATIVE STANDARD ERRORS FOR ESTIMATES OF
  PERCENTS, 1988 THROUGH 1996

  Approximate relative standard errors for estimates of percents may be calculated from the
  tables in Appendix D also.  The relative standard error for a percent, 100 * p (0<p<1),
  may be calculated using the formula:

       RSE(p) = SQRT [b * (1 - p)/(p * X)]

  where 100 * p is the percent of interest, X is the base of the percent, and b is the
  parameter b in the formula for approximating the RSE(X).  Values for b are given in the
  accompanying files.

  For example, in 1992 the estimated number of discharges from short-stay hospitals which
  were female was 18,545,000.  This is 59.9 percent of the estimated 30,951,000 discharges
  for that year.  Using the file, RSE92.WK1, in Appendix D for estimates by sex, the value
  of b is 404.530.  Thus,

       RSE(.599) = SQRT [404.530 * (1 - .599) / (.599 * 30,951,000)]  = 0.00296

  The relative standard error for the estimate of interest is 0.00296.  Expressed as a percent,
  RSE(.599) = .296%.  From this the standard error is obtained by multiplying the relative
  standard error by the estimate:

       SE(.599) = .599 * 0.00296 = 0.00177.

  The standard error can be employed to generate confidence intervals for statistical testing,
  as shown above.

  COMPUTATION OF  RELATIVE STANDARD ERRORS OF RATES IN WHICH THE
  DENOMINATOR HAS NO SAMPLING ERROR

  It is generally assumed that population estimates which are obtained from the Bureau of
  the Census for certain overall totals, such as the U.S. population and subgroups
  disaggregated by age, sex, race, and region, are not subject to sampling error or that the
  error may be small enough to be considered negligible.  The relative standard error of
  rates formed with these populations as the denominator is the relative standard error of
  the numerator.  Thus, to obtain the standard error of the rate, simply multiply the rate
  itself by the RSE of the numerator.

  COMPUTATION OF RELATIVE STANDARD ERRORS FOR MULTIPLE YEAR
  ESTIMATES, 1979 THROUGH 1996

  This section presents procedures which may be used to approximate sampling errors of
  estimates based on multiple years of data collected under either or both of the 1965 and
  1988 NHDS sample designs.  These procedures are not considered final.  However, they
  will permit approximating variances for multi-year estimates until research into
  potentially improved methods can be completed for estimates based on the 1988 sample
  design.  It is believed the approximations are conservative and, hence, should not indicate
  significance when the contrary is actually true.

  VARIANCE OF ESTIMATED TOTALS FOR MULTIPLE YEARS

  For discussion purposes, let X' equal the multi-year aggregate estimate for the
  characteristic of interest.  That is,

       X' = sum of annual aggregate estimates for any characteristic of interest 
               for any number of years (say, Y years)

  If the annual estimates are all from years between 1965 and 1987, then

       X'65 = sum of annual aggregate estimates for any characteristic of interest
            for any number of years between 1965 and 1987

  If the annual estimates are all from years between 1988 and the present, then

       X'88 = sum of annual aggregate estimates for any characteristic of interest
            for any number of years between 1988 and 1996

  If the annual estimates are from years in both the 1965 and 1988 samples, then

       X' = X'65 + X'88

  The procedure for approximating the variance of X'  differs depending on the set Y of
  years in the database for X'.

  SITUATION A.  
  When the data base includes only years from the period 1965-1987, the following formula
  is used:

       VAR(X'65) = (X'65)^2 * [RSE(X'65|Y years)]^2                                        (1)

  where

       RSE(X'65|Y years) = [SQRT (R|Y years)] * max [RSE (X'65|1 year)]        (2)

  and
       max [RSE (X'65|1 year)] = maximum relative standard error over Y years
                                 calculated as though X'65 were based only on data
                                 from the single year, y.

  (Instructions for determining the RSE for a single year estimate are given above.)

  The value R in (2) above is calculated as follows.  
  (Attachment D1 in this Appendix presents a derivation of the R factor).

       R|Y years = (alpha * average-n) + 500                                                      (3)
                    alpha * (average-n + 500)

       where 
            alpha = the number of years from the 1965-1987 period which are
                 included in the data base for X'65

            average-n = the average number of sampled discharges per hospital 
                        per year in the data base for X'65 (Attachment D1 explains
                        the calculation of average-n).

  For example, assume an estimated 10,000 discharges during the data years 1986-1987
  were to patients receiving surgery "S" during their stays.  Here,

       X'65 = 10,000 discharges, Y = {1986, 1987}, and alpha = 2.

       RSE (X'65|1 year, 1986) = .102   (From published RSE curves)

       RSE (X'65|1 year, 1987) = .105   (From published RSE curves)

  Hence, max [RSE (X'65|1 year)] = max [.102, .105] = .105

  Using data from Attachment D2 in this Appendix, the average number of discharges per
  respondent hospital per year is calculated as:

       average-n = 193,000 + 181,000    = 457.2
                   ___________________
                          418 + 400

   The use of alpha and the above in equation (3) gives:

       R|Y years = (alpha * average-n) + 500 = 2 (457.2) + 500 = 1,414.4 = .739
                    ____________________________________________________
                    alpha * (average-n + 500)    2 (457.2 + 500)    1,914.4

  Substituting in equation (2),

       RSE(X'65|2 years) = [SQRT (.739)] * .105 = .09

  And, by equation (1), the variance of the multi-year aggregate X'65 is

       Var(X'65|years 1986 & 1987) = {[(10,000)^2] * [(.09)^2]} = 810,000.

  SITUATION B.  
  When the data base includes only years from the period 1988 through the present, then
  equation (1) above is used, but the calculation of the single year RSE is different.  The
  following formula is used to the calculate the RSE of any single year estimate from 1988
  through 1996.

       RSE(X'88 |1 year) = SQRT (a + b/X)                                                          (4)

  The parameters a and b are given in the files accompanying this document.
  (This approximation for the variance of X'88 ignores any reductions in the variance which
  may result from relationships between the first, second, and third stage components in the
  variance when estimates are based on the 1988 NHDS sample design.  That relationship
  and the magnitude of its effects on the variances is unknown at this writing.)

  For example, assume an estimated 10,000 discharges during the data years 1988-1989
  were to patients receiving surgery "S" during their stays.  Here,

       X'88 = 10,000 discharges,  Y = {1988, 1989}, and alpha = 2.

  Using equation (4) above, the following is obtained:

  Year    a            b            RSE(10,000)                                                                
  ______________________________________________________________________________
  1988  .001591421    403.123981    0.2047   (based on 1988 Data Tape Documentation)
  1989  .0029026252   478.865192    0.2254   (based on 1989 Data Tape Documentation)

  Hence,

       max [RSE (X'88|1 year)] = max [.2047, .2254] = .2254

  And, by equation (1), the variance of the multi-year aggregate X'88 is

       Var(X'88|years 1988 & 1989) = [(10,000)^2] * [(0.2254)^2] = 5,080,516

  
  SITUATION C.  
  When the data base Y includes years from both the 1965-1987 and the 1988-1996
  periods, the estimate X' and the data base set of years Y may be written as:

       X' = X'65 + X'88  and

       Y = Y65 + Y88

  where the X' and Y denote, respectively, the multi-year estimate and the set of years when
  data collection is restricted to either the '65 sample design or the '88 sample design.

  Then, because the two samples were selected independently of each other, the variance
  becomes

       Var(X') = Var(X'65) + Var (X'88) ,                                                             (5)

  Use the procedures given above to approximate Var(X'65) and Var (X'88).

  For example, assume an estimated 10,000 discharges had surgery "S" during the data
  years 1986-1987 and another 10,000 discharges had surgery "S" during the data years
  1988-1989.

  Here,

       X' = X'65 + X'88 = 10,000 + 10,000 = 20,000 discharges

       Y = Y65 + Y88 = {1986, 1987} + {1988, 1989} and

       alpha  = 4.

  From the examples in situations A and B,

       VAR(10,000|years 1986 and 1987) = 810,000 
       VAR(10,000|years 1988 and 1989) = 5,080,516

  Hence, by equation (5), the variance for the multi-year aggregate X' is:

       VAR(20,000|years 1986-1989) = 810,000 + 5,080,516 = 5,890,516

  VARIANCES OF ESTIMATED AVERAGE ANNUAL TOTALS

  The variance for an average annual total is derived by first approximating the variance for
  X', according to the instructions for the multi-year aggregate estimate.  Then, let

       X' / alpha = the average annual aggregate for the characteristic of interest 
                   for alpha years of data

  where

       X' =  the multi-year aggregate estimate for the characteristic of interest
  and
       alpha = the total number of years included in the data base for X' 
                   (that is, the number of years in the set of Y years).

  Then, the variance for the estimated average annual aggregate is:

       VAR (X' / alpha) = VAR(X') / (alpha)^2                                                (6)

  SITUATION A.  
  For the average annual aggregate per year, when the data years are all between 1965 and
  1987, using the example cited above,

       X'65 / 2 = 10,000 / 2 = 5,000.

  Substituting in equation (6) gives the variance of  X'65 / 2:

       VAR(X'65 / 2 | years 1986, 1987) = VAR (X'65) / 2^2   
                                  = 810,000 / 2^2 
                                  = 202,500

  SITUATION B.  
  For the average annual aggregate per year, when the data years are all between 1988 and
  1996, using the example cited above,

        X'88 / 2 = 10,000 / 2 = 5,000

  Substituting in equation (6) gives the variance of  X'88 / 2:

       VAR(X'88 / 2 | years 1988, 1989) = VAR (X'88) / 2^2  
                                  = 5,080,516 / 2^2 
                                  = 1,270,129

  SITUATION C.  
  For the average annual aggregate per year, when the data years included are from both the
  1965 design and the 1988 redesign, using the example cited above,

       X' / 4 = 20,000/4 = 5,000

  Substituting in equation (6) gives the variance of  X' / 4:

       VAR(X' / 4 | years 1986, 1987, 1988, 1989)  = VAR (X') / 4^2 
                                     =  5,890,516 / 4^2 
                                     =  368,157

    ATTACHMENT D1.  Factor R for Approximating Rel-variances for  Multi-year
  Estimates from the 1965 NHDS Sample Design.

  Here, it is assumed the multi-aggregate estimate X' is based on data collected in the
  NHDS during two or more of the years 1965-1987.  Then the rel-variance of X'65 may be
  approximated by

       RSE^2(X'65|Y years) = R * max [RSE^2(X'65|1 year)]

  where

       X'65 = the multi-year aggregate estimate of interest.

       Y = the set of years in the data base for X'65.

       RSE^2(X'65) = the rel-variance of X'65.

  For simplicity, assume that the number of sampled hospitals and sampled discharge
  abstracts in the NHDS remain constant over the data years that serve as the reference
  period for the estimate X'65.  Also assume that the total number of abstracts submitted to
  NHDS each of those years is constant.  Let:

       m = the number of hospitals participating in the NHDS

       n = the number of sample abstracts in the NHDS each year

       B = the between hospital rel-variance for the population of  discharges

       W = the within hospital rel-variance for the population of  discharges

       alpha  = the number of years in the data base Y

  A streamlined approximation to the rel-variance of  X'65 based on a single year of data is
  then

       RSE^2(X'65|1 year)   = (B^2 / m) + (W^2 / n) = B^2 {(1 / m) + [(W / B) / n]}

  During the original work on the NHDS design, values of the ratio W/B were determined
  and found to lie in the range of 300 - 700 with some concentration near 500 (NCHS
  Report Series 2, Number 39).  Hence, for the general statistic, the effect of using alpha
  years of data can be roughly approximated by setting W/B equal to 500.  Then the
  rel-variance for one year of data is approximately

       RSE^2(X'65|1 year) = B^2 [(1 / m) + (500 / n)]

  and the rel-variance for estimates based on alpha years of data is approximately

       RSE^2(X'65|alpha years) = B^2 [(1 / m) + (500 / (alpha*n))]

  The ratio of the two rel-variances can thus be formulated as:

       RSE^2(X'65|alpha years)    =   (alpha * (n / m)) + 500   =   R
       ______________________          ______________________
         RSE^2(X'65|1 year)            alpha * ((n / m) + 500)

  Because in reality, sample sizes can vary across the Y years, the average number of
  sampled abstracts per hospital per year over the Y years in the data base is used in place
  of n/m in R.   That is, in place of n/m, use average-n which is defined as:

       average-n =    the total number of sampled discharges over
                      the years included in the data base (n), 
                      divided by the sum of the  number of
                      respondent hospitals over the same time
                      period (m).   NOTE: the number of sampled
                      discharges per year and the number of
                      respondent hospitals per year appear in
                      Attachment D2.

  Hence,

       R = (alpha * average-n) + 500
           _________________________
           (alpha * (average-n + 500)

ATTACHMENT D2:  Numbers of hospitals participating in NHDS and approximate total
  number of sampled discharge abstracts, by year *

DATA YEAR	NUMBER OF HOSPITALS	APPROXIMATE NUMBER OF SAMPLED DISCHARGE ABSTRACTS

1965	296	100,000
1966	300	137,000
1967	289	145,000
1968	413	210,000
1969	402	208,000
1970	395	205,000
1971	179	200,000
1972	424	225,000
1973	424	225,000
1974	426	227,000
1975	432	232,000
1976	419	223,000
1977	423	224,000
1978	413	219,000
1979	416	215,000
1980	420	224,000
1981	428	227,000
1982	426	214,000
1983	418	206,000
1984	407	192,000
1985	414	195,000
1986	418	193,000
1987	400	181,000
1988	422	250,000
1989	408	233,000
1990	474	266,000
1991	484	274,000
1992	494	274,000
1993	466	235,000
1994	478	277,000
1995	466	263,000
1996	480	282,000

*  From Series 13 reports on Utilization of Short Stay Hospitals in the U.S.A.  LOTUS tables to accompany Appendix D:

  RSE79.WK1  -- Approximate relative standard errors of estimated statistics, 1979
  RSE80.WK1  -- Approximate relative standard errors of estimated statistics, 1980
  RSE81.WK1  -- Approximate relative standard errors of estimated statistics, 1981
  RSE82.WK1  -- Approximate relative standard errors of estimated statistics, 1982
  RSE83.WK1  -- Approximate relative standard errors of estimated statistics, 1983
  RSE84.WK1  -- Approximate relative standard errors of estimated statistics, 1984
  RSE85.WK1  -- Approximate relative standard errors of estimated statistics, 1985
  RSE86.WK1  -- Approximate relative standard errors of estimated statistics, 1986
  RSE87.WK1  -- Approximate relative standard errors of estimated statistics, 1987
  RSE88.WK1  -- Estimated parameters for relative standard errors equations 
                 by selected patient and hospital characteristics, 1988
  RSE89.WK1  -- Estimated parameters for relative standard errors equations 
                 by selected patient and hospital characteristics, 1989
  RSE90.WK1  -- Estimated parameters for relative standard errors equations 
                 by selected patient and hospital characteristics, 1990
  RSE91.WK1  -- Estimated parameters for relative standard errors equations 
                 by selected patient and hospital characteristics, 1991
  RSE92.WK1  -- Estimated parameters for relative standard errors equations 
                 by selected patient and hospital characteristics, 1992
  RSE93.WK4  -- Estimated parameters for relative standard errors equations 
                 by selected patient and hospital characteristics, 1993
  RSE94.WK4  -- Estimated parameters for relative standard errors equations 
                 by selected patient and hospital characteristics, 1994
  RSE95.WK4  -- Estimated parameters for relative standard errors equations 
                 by selected patient and hospital characteristics, 1995
  RSE96.WK4  -- Estimated parameters for relative standard errors equations 
                 by selected patient and hospital characteristics, 1996

APPENDIX E

  This appendix describes the files included on the diskette accompanying this
  documentation, which contain Census Bureau estimates of the U. S. civilian resident
  population, as of July 1, for the years 1979 through 1996.  There are two types of files,
  named either 1YRxx.WK1 or REGxx.WK1.  To select a given year, the "xx" can be
  replaced by the last two-digits of the year desired between 1979 and 1996 (e.g. 79). 
  These estimates are consistent with the population estimates published in Current
  Population Reports, Series P-25.  For the years 1980 through 1996, there are separate
  tables for estimates disaggregated by sex, race, and single-year age groupings and those
  disaggregated by sex, region, and single-year age groupings.  These population estimates
  have been adjusted based on the 1990 decennial census.

  There is only one spreadsheet for 1979 because data disaggregated by region are not
  available for this year.  Also the figures in the 1979 spreadsheet have been rounded to the
  nearest thousand, whereas those for all the other years are unrounded.  The 1979 data
  were adjusted based on the 1980 Census.

  It should be noted that rates calculated with these estimates may differ slightly from those
  in published NCHS reports or those calculated from population estimates disseminated
  with the NHDS annual data tape documentation.  Before 1981, estimates of rates of
  discharges and days of care which appeared in published reports from NCHS were
  calculated using the civilian noninstitutional population.  However, beginning in 1981,
  the civilian resident population estimates were used.  The civilian resident population was
  determined to be more appropriate because persons in institutions, for example nursing
  home patients, are hospitalized when necessary.  A report has been published which
  discusses differences in discharge rates based on the different denominators (see
  Reference 9 in documentation).

  LOTUS tables to accompany Appendix E

  1YR79.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Race, July 1, 1979
  1YR80.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Race, July 1, 1980
  1YR81.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Race, July 1, 1981
  1YR82.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Race, July 1, 1982
  1YR83.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Race, July 1, 1983
  1YR84.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Race, July 1, 1984
  1YR85.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Race, July 1, 1985
  1YR86.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Race, July 1, 1986
  1YR87.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Race, July 1, 1987
  1YR88.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Race, July 1, 1988
  1YR89.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Race, July 1, 1989
  1YR90.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Race, July 1, 1990
  1YR91.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Race, July 1, 1991
  1YR92.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Race, July 1, 1992
  1YR93.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Race, July 1, 1993
  1YR94.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Race, July 1, 1994
  1YR95.WK4 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Race, July 1, 1995
  1YR96.WK4 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Race, July 1, 1996

  REG80.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Region, July 1, 1980
  REG81.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Region, July 1, 1981
  REG82.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Region, July 1, 1982
  REG83.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Region, July 1, 1983
  REG84.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Region, July 1, 1984
  REG85.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Region, July 1, 1985
  REG86.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Region, July 1, 1986
  REG87.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Region, July 1, 1987
  REG88.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Region, July 1, 1988
  REG89.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Region, July 1, 1989
  REG90.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Region, July 1, 1990
  REG91.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Region, July 1, 1991
  REG92.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Region, July 1, 1992
  REG93.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Region, July 1, 1993
  REG94.WK1 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Region, July 1, 1994
  REG95.WK4 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Region, July 1, 1995
  REG96.WK4 -- Civilian Population of the United States,
                Estimates by Age, Sex, and Region, July 1, 1996

APPENDIX F
  
  The following tabulations are provided for the purpose of verifying that data processing
  of the multi-year file is accurate.  Included are tables of estimated discharges,
  disaggregated by sex, age groups, race, discharge status, and region; estimated days of
  care; estimated numbers of selected first-listed and all-listed diagnoses; estimated
  numbers of selected all-listed procedures; and estimated newborn infant discharges,
  disaggregated by sex, region, and health status.  Note that these are weighted frequencies,
  which were produced by applying the weight variable (columns 21-25) to the analysis.

FREQUENCIES FOR NON-NEWBORNS, NHDS, 1979-1996
DATA YEAR	TOTAL DISCHARGES	TOTAL DAYS OF CARE	MALE	FEMALE	UNDER 15	15-44	45-64	65 & UP

1979	36,746,563	264,173,219	14,704,807	22,041,756	3,641,112	15,487,593	8,532,087	9,085,771
1980	37,831,559	274,508,358	15,145,249	22,686,310	3,672,493	15,635,443	8,659,807	9,863,816
1981	38,543,980	277,229,888	15,379,076	23,164,904	3,733,060	15,725,148	8,677,432	10,408,340
1982	38,593,355	272,626,923	15,469,954	23,123,401	3,654,396	15,553,926	8,688,003	10,697,030
1983	38,782,663	268,337,331	15,573,018	23,209,645	3,653,950	15,268,547	8,558,436	11,301,730
1984	37,162,124	244,651,694	14,899,095	22,263,029	3,208,176	14,532,906	8,194,831	11,226,211
1985	35,056,134	226,217,043	14,160,466	20,895,668	2,971,825	13,966,558	7,609,571	10,508,180
1986	34,255,915	218,496,028	13,949,308	20,306,607	2,782,612	13,457,746	7,299,897	10,715,660
1987	33,386,694	214,942,242	13,568,200	19,818,494	2,687,520	13,141,509	7,099,013	10,458,652
1988	31,146,360	203,677,561	12,641,965	18,504,395	2,610,430	11,933,540	6,456,122	10,146,268
1989	30,946,718	200,826,678	12,583,154	18,363,564	2,597,343	11,848,274	6,271,496	10,229,605
1990	30,787,939	197,421,786	12,279,604	18,508,335	2,411,674	11,798,790	6,244,267	10,333,208
1991	31,098,002	199,098,663	12,478,352	18,619,650	2,498,479	11,620,374	6,173,130	10,806,019
1992	30,950,912	190,385,530	12,406,079	18,544,833	2,531,414	11,226,701	6,328,830	10,863,967
1993	30,825,148	184,601,125	12,262,445	18,562,703	2,141,152	11,200,025	6,283,434	11,200,537
1994	30,843,087	177,178,999	12,293,339	18,549,748	2,249,317	10,956,147	6,311,114	11,326,509
1995	30,722,351	164,626,802	12,197,504	18,524,847	2,405,422	10,593,181	6,167,656	11,556,092
1996	30,544,614	159,882,807	12,109,749	18,434,865	2,206,856	10,325,208	6,294,238	11,718,312

FREQUENCIES FOR NON-NEWBORNS, NHDS, 1979-1996
DATA YEAR	NORTH-EAST	MIDWEST	SOUTH	WEST	WHITE	BLACK	ALL OTHER RACES	RACE NOT STATED

1979	7,785,635	10,647,226	12,424,987	5,888,715	27,450,925	3,957,844	-	5,337,794
1980	7,868,414	10,877,714	12,982,849	6,102,582	28,484,009	4,176,172	702,456	4,468,922
1981	7,821,859	11,131,851	13,202,327	6,387,943	32,242,003	5,003,852	1,298,125	-
1982	7,847,372	10,937,996	13,435,287	6,372,700	29,879,874	4,216,328	926,139	3,571,014
1983	7,792,914	10,492,289	13,883,629	6,613,831	30,106,094	4,254,555	980,708	3,441,306
1984	7,407,768	9,899,132	13,450,674	6,404,550	28,448,523	4,265,667	1,035,836	3,412,098
1985	7,168,298	9,111,370	12,274,465	6,502,001	26,378,763	4,109,162	1,071,573	3,496,636
1986	6,955,118	8,930,808	11,892,160	6,477,829	25,363,328	4,015,423	1,100,707	3,776,457
1987	6,698,861	8,718,351	11,291,607	6,677,875	24,375,931	3,866,448	1,308,034	3,836,281
1988	7,078,483	7,832,097	10,844,990	5,390,790	23,321,644	3,828,797	1,179,155	2,816,764
1989	7,044,102	7,675,518	10,959,504	5,267,594	22,677,616	3,891,025	976,405	3,401,672
1990	6,895,148	7,620,112	11,173,053	5,099,626	21,375,856	3,611,203	958,238	4,842,642
1991	7,153,072	7,315,173	11,289,656	5,340,101	20,816,245	3,717,049	1,036,368	5,528,340
1992	7,140,865	7,121,396	11,255,745	5,432,906	20,017,886	3,692,237	1,127,549	6,113,240
1993	6,964,731	7,097,084	11,580,414	5,182,919	20,101,017	3,659,646	1,252,661	5,811,824
1994	7,128,436	7,133,439	11,310,254	5,270,958	20,003,156	3,711,210	1,351,413	5,777,308
1995	7,051,480	6,994,250	11,373,398	5,303,223	19,950,723	3,887,498	1,097,619	5,786,511
1996	6,665,339	7,106,564	11,085,190	5,687,521	19,738,155	3,779,331	1,351,228	5,675,900

CATEGORY OF ALL-LISTED DIAGNOSES	TOTAL DIAGNOSES	SEPTICEMIA	MALIGNANT NEOPLASMS	DIABETES MELLITUS	PSYCHOSES	ACUTE MYOCARDIAL INFARCTION	ASTHMA	INJURY & POISONING
ICD-9-CM DIAGNOSIS CODES:	ALL CODES, EXCEPT E-CODES	038	140-208, 230-234	250	290-299	410	493	800-999

1979	86,117,260	157,201	2,887,931	2,136,178	844,025	688,256	512,964	6,390,512
1980	90,397,405	167,298	3,011,597	2,279,410	860,709	683,416	603,863	6,435,257
1981	94,364,901	179,721	3,197,975	2,395,492	965,847	772,357	627,926	6,476,685
1982	97,720,714	209,174	3,261,378	2,562,028	1,020,657	785,267	664,081	6,447,751
1983	101,968,881	256,814	3,284,594	2,774,733	1,073,172	784,672	708,607	6,340,400
1984	104,260,914	325,239	3,815,918	2,940,819	1,216,067	811,099	738,631	6,555,550
1985	100,716,114	376,900	3,739,439	2,756,904	1,336,485	870,981	742,906	6,426,072
1986	102,763,567	433,149	3,744,660	2,863,645	1,472,944	869,982	780,493	6,369,803
1987	103,431,392	438,527	3,768,126	2,901,699	1,562,034	872,189	784,536	6,353,854
1988	100,650,053	473,053	3,547,167	2,917,796	1,527,293	818,819	827,683	6,066,482
1989	101,974,483	482,964	3,588,880	2,929,710	1,568,434	797,551	835,203	5,939,040
1990	102,833,929	479,603	3,457,063	3,007,518	1,635,736	785,806	861,036	6,039,311
1991	106,907,515	516,821	3,604,767	3,304,513	1,846,023	809,233	923,066	6,059,732
1992	109,298,647	564,740	3,598,145	3,539,249	1,974,622	830,183	955,659	5,927,373
1993	112,792,664	551,449	3,486,860	3,669,661	2,218,577	839,502	999,768	6,013,845
1994	115,706,869	553,182	3,403,488	3,740,073	2,549,059	865,039	1,053,348	5,972,407
1995	118,254,675	587,651	3,472,180	3,952,279	2,544,787	857,664	1,176,094	5,965,231
1996	121,711,665	661,377	3,502,145	4,157,040	2,611,842	919,247	1,183,413	5,918,968

CATEGORY OF ALL-LISTED PROCEDURES	TOTAL PROCEDURES	CESAREAN SECTION	HYSTERECTOMY	CABG	PROSTATECTOMY	APPENDECTOMY
ICD-9-CM PROCEDURE CODES	ALL CODES	740-, 741-, 742-, 744-, 7499	683-687	361	602-606	470

1979	29,602,619	599,140	638,898	114,002	292,958	311,043
1980	31,411,526	619,499	649,446	137,145	334,946	290,594
1981	33,635,312	701,616	672,706	159,471	347,996	311,821
1982	34,632,285	730,339	649,998	170,117	358,306	276,638
1983	35,938,870	807,513	672,254	191,308	356,830	282,080
1984	36,155,105	812,661	664,487	202,212	361,119	294,242
1985	36,759,878	876,753	670,332	230,353	366,804	283,156
1986	38,000,321	905,616	644,188	284,464	366,713	275,192
1987	39,118,398	952,615	654,595	331,793	410,132	302,811
1988	39,191,713	933,397	578,346	352,942	357,537	272,980
1989	40,042,644	937,899	540,665	368,210	376,315	252,749
1990	40,505,676	945,330	591,066	392,111	363,789	273,725
1991	43,922,460	933,325	546,341	407,353	363,472	254,992
1992	42,627,290	920,872	579,966	468,354	352,706	260,804
1993	41,608,334	917,313	561,693	485,399	317,184	250,084
1994	40,710,173	858,417	555,987	501,210	262,551	279,774
1995	39,807,237	784,856	582,778	573,133	239,255	237,126
1996	40,397,052	835,136	590,740	598,288	202,547	262,503

FREQUENCIES FOR NEWBORN INFANTS, NHDS, 1979-1996

DATA YEAR	TOTAL	MALE	FEMALE	NORTHEAST	MIDWEST	SOUTH	WEST	SICK BABY	WELL BABY

1979	3,680,008	1,906,207	1,773,801	718,022	1,028,740	1,246,884	686,362	928,339	2,751,669
1980	3,823,935	1,949,729	1,874,206	735,271	1,043,176	1,315,209	730,279	1,008,116	2,815,819
1981	3,841,360	1,987,109	1,854,251	731,516	1,031,989	1,302,700	775,155	1,044,165	2,797,195
1982	3,926,071	2,019,681	1,906,390	733,230	1,002,579	1,404,114	786,148	1,092,820	2,833,251
1983	3,828,449	1,971,712	1,856,737	716,646	953,156	1,387,511	771,136	1,098,875	2,729,574
1984	3,857,445	2,002,965	1,854,480	688,886	938,452	1,447,418	782,689	1,166,936	2,690,509
1985	3,793,931	1,953,429	1,840,502	665,177	908,868	1,363,567	856,319	1,318,788	2,475,143
1986	3,751,460	1,953,620	1,797,840	685,520	910,701	1,250,755	904,484	1,374,505	2,376,955
1987	3,970,798	2,032,577	1,938,221	699,899	937,561	1,340,844	992,494	1,536,195	2,434,603
1988	3,732,535	1,881,926	1,850,609	736,577	887,419	1,226,961	881,578	1,511,288	2,221,247
1989	3,884,481	1,989,462	1,895,019	751,647	952,751	1,269,061	911,022	1,628,006	2,256,475
1990	3,869,089	1,981,939	1,887,150	732,771	905,076	1,323,844	907,398	1,541,839	2,327,250
1991	3,879,666	2,002,719	1,876,947	714,390	876,902	1,333,637	954,737	1,586,489	2,293,177
1992	3,688,513	1,926,108	1,762,405	684,583	806,457	1,264,024	933,449	1,510,035	2,178,478
1993	3,578,666	1,823,043	1,755,623	689,268	793,118	1,289,740	806,540	1,442,161	2,136,505
1994	3,749,285	1,934,737	1,814,548	751,139	816,617	1,315,455	866,074	1,738,328	2,010,957
1995	3,630,558	1,872,083	1,758,475	699,331	785,845	1,321,036	824,346	1,462,035	2,168,523
1996	3,925,871	1,998,799	1,927,072	645,439	825,932	1,403,164	1,051,336	1,489,640	2,436,231

This page last reviewed: Friday, July 13, 2007

This information is provided as technical reference material. Please contact us at cwus@cdc.gov to request a simple text version of this document.

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