FAQs -- Frequently Asked Questions

This page contains answers to common questions handled by our support staff, along with some tips and tricks that we have found useful.


CDC WONDER: Information and Communication

Wide-ranging ONline Data for Epidemiologic Research (WONDER) -- is an easy-to-use internet system that makes the information resources of the Centers for Disease Control and Prevention (CDC) available to public health professionals and the public at large. It provides access to a wide array of public health information.

CDC WONDER furthers CDC's mission of health promotion and disease prevention by speeding and simplifying access to public health information for state and local health departments, the Public Health Service, and the academic public health community. CDC WONDER is valuable in public health research, decision making, priority setting, program evaluation, and resource allocation.

CDC WONDER, developed by the Centers for Disease Control and Prevention (CDC), is an integrated information and communication system for public health. Its purposes are:

  1. To promote information-driven decision making by placing timely, useful facts in the hands of public health practitioners and researchers, and
  2. To provide the general public with access to specific and detailed information from CDC.

With CDC WONDER you can:

  • Search for and read published documents on public health concerns, including reports, recommendations and guidelines, articles and statistical research data published by CDC, as well as reference materials and bibliographies on health-related topics;
  • Query numeric data sets on CDC's information systems, via "fill-in-the blank" web pages. Public-use data sets about mortality (deaths), cancer incidence, HIV and AIDS, TB, natality (births), census data and many other topics are available for query, and the requested data are readily summarized and analyzed. Produce tables, maps, charts and download tab-delimited text exports of summary statistics.
The data is ready for use in desktop applications such as word processors, spreadsheet programs, or statistical and geographic analysis packages. File formats available include web pages (HTML), chart and map images (bitmaps] and spreadsheet files (ASCII with Tab Separated Values). All of these facilities are menu-driven, and require no special computer expertise.

To learn more about our services, please contact us.

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How do I get a quick start with using the features and screens?

See the Quick Start Guide for help with using the functions.

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How can I find a certain dataset that I heard was available on CDC WONDER?

CDC WONDER's "home" page provides three ways to find the information you are seeking:

  • Descriptive titles are categorized under topic and headings;
  • The alphabetical index includes the descriptive title, the official name and the acronym for each data item;
  • The "Search" feature finds pages that contain a specific word or phrase.
We are always glad to add more data to WONDER. Please contact us with your suggestions!

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Why are some data requests returned right away, while other requests take longer?

Some data requests result in very large data results sets, and your computer may take more time to download and view the data. The number of variables in a request also affects the response time. For example, a database query with several specific disease code ranges and sorted by disease or sorted by year may require more processing time. You can increase the amount of time for the query to run in the last section on any WONDER data request screen. The default value is 10 minutes, the maximum value is 15 minutes. If the results to your query are not returned within 15 minutes, then please contact us with your specific query criteria for assistance.

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How are small data values protected to avoid revealing the identities of individual people?

In order to protect personal privacy, and to prevent revealing information that may identify specific individuals, small data values are not available in some circumstances. Incidence counts and corresponding rates and other measures are not revealed when the count falls below a ratio of the representative demographic population. WONDER protects small values in the following ways:

  1. The label "Suppressed" is displayed when counts fall below the determined "cut-off" value and the conditions for suppression are met.
  2. Rows showing Totals and sub-totals, are not available when only one row in the results table is suppressed for any summarized section of the table. If an aggregate value represents more than one suppressed row, then sub-totals and totals are available when allowed. If the sub-totals or total values fall within the privacy policy, then these values are also suppressed as applicable.
  3. The Percentage of Total column is not shown when any single row in the results table is suppressed. Note that not all of the online databases report the Percentage of Total measure.
  4. Rows that contain suppressed measures are not sorted by the actual suppressed data value. When the results table is ordered by a column that contains suppressed values, the suppressed values are displayed as though the value was less than zero, instead of showing the suppressed values in the actual sequential numeric order in the table. For example, when data for a specific county are suppressed, and you choose to order the data by rate, then the row representing that county is displayed in the rate value sequence as though the suppressed value was less than zero. The actual suppressed values in the hidden rows are included in the aggregate total values, when totals and sub-totals are displayed.

The "privacy policy" defines the suppression threshold and the specific rules that set the circumstances for when suppression is applied. The privacy policies vary from dataset to dataset. For example, some datasets only suppress county level data when the total population falls below a threshold value, other datasets only suppress data for certain small demographic groups. The policy is determined for each dataset by the data provider in compliance with federal and local privacy regulations. For details on a specific dataset's privacy policy and suppression rules, refer to the documentation for that dataset, or select Help on the dataset's query page. For more information on federal privacy policies, see Data Use Restrictions.

When a larger population, time period or geographic area is selected, fewer values are likely to be suppressed. Some statisticians make use of data smoothing algorithms to reduce the impact of suppressed data. For example, please see "The Impact of Data Suppression on Local Mortality Rates:  The Case of CDC WONDER" by Chetan Tiwari, Kirsten Beyer, and Gerard Rushton, published in American Journal of Public Health, Vol. 104, No. 8: 1386-1388. Available at http://ajph.aphapublications.org/doi/abs/10.2105/AJPH.2014.301900.

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What exactly are age-adjusted rates?

The rates of almost all causes of disease, injury, and death vary by age. Age adjustment is a technique for "removing" the effects of age from crude rates so as to allow meaningful comparisons across populations with different underlying age structures. For example, comparing the crude rate of heart disease in Florida with that of California is misleading, because the relatively older population in Florida leads to a higher crude death rate, even if the age-specific rates of heart disease in Florida and California were the same. For such a comparison, age-adjusted rates are preferable.

Age-adjusted rates are calculated by applying the age-specific rates of various populations to a single standard population. In CDC WONDER, if you choose to age-adjust rates, you must specify your standard population (or accept the default). It is good practice to specify a standard is that generally similar to the populations being compared. For example, if requesting breast cancer mortality rates for white females in Massachusetts for the period 1979-1991, you might specify "1985 Massachusetts white females" as your standard population.

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How do I find the citation for data from WONDER?

Each WONDER online database shows the suggested citation in the online "help" file, and also on each screen that displays results for your data request. Look near the end of the page below your table, chart or map to find the suggested citation. Each suggested citation shows the data source, with agency names, data set names and specific release identification when applicable. The date and time of your data query are also shown. If you download data using the export feature, the citation is in the first column, below the numeric values.

When citing written material from a web page, include the web address and the date of access. Use the web address of the first page for citing the online databases, because addresses of the subsequent pages are dynamic after a query occurs.

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How do I get permission to use, share, copy or publish information from WONDER?

CDC WONDER is a public service developed and operated by the Centers for Disease Control and Prevention, an agency of United States federal government. The public web site at http://wonder.cdc.gov is in the public domain, and only provides access to public use data and information. You may access the information freely, and use, copy, distribute or publish this information without additional or explicit permission. Please do provide a citation to credit the authors and/or data providers. When referring to a written article or document, please cite the item as you would any other document on the world wide web.

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How do I consent to the data use agreement for data in WONDER?

Any use or access of the data and information available in WONDER implies your consent to our data use agreement. Review the Data Use Restrictions carefully before using WONDER. All data are covered by the provisions of the Public Health Service Act (42 U.S.C. 242m(d)) .

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How do I "save" a query or output in CDC WONDER, to use later or to share with others?

Use the Save button, located in upper right corner on the WONDER online databases, to save your work for later, or to share a link to your work with others. After you click the "Save" button, you will see a message telling you that your query has been saved in the WONDER System. You can do two things:

  • Press Ctrl+D to Bookmark your saved page or Add it to Favorites. This action saves the link in your web browser, so you can use it later. When you use it later, first it sends a request with your saved query criteria. If you clicked on the Save button on the Results, Chart or Map tabs, then it will stop at the page that was saved, showing the current results, chart or map.
  • You can also use the Share button on the message to pop up a link to the saved page. You can send this link to others, or share the link in a web page.
When you're done, click the Resume Current Work button below the message to return to your session with a WONDER online database.

When you use a saved request later, a message will tell you if your saved query pulls data from a data set that has been updated. If the updated data are stored in a separate online database, the message will show you to the link to the updated data. For more information, see "How do I save my data for later use?."

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How do I download WONDER numerical data into statistical software, spreadsheets, or graphical packages such as Epi Info, on my PC?

After requesting numeric data, you may wish to load the data results into a spreadsheet or statistical analysis program. Most analysis software packages can load delimited simple text, when the rows and columns are separated by tabs. If your software has trouble importing a delimited file, you may wish to remove the citation and other reference text included in the file in the first column, below the numeric values.

WONDER data requests show the results as web pages (HTML) by default. Tab-delimited simple text format files are also available for download with the export feature.

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How are implicitly related data concepts handled in WONDER?

Some of the data stored in the CDC WONDER online databases have implicit relationships or connections to other data. For example, specific counties are located within certain states and regions. When you limit data to Delaware and group results by County, you see data for the counties within Delaware. In the mortality online databases, causes of death are categorized in several ways, such as International Classification of Disease (ICD) codes, or as drug and alcohol-related causes, or as Injury Intent categories. When data are grouped by Cause of Death specified as ICD Codes, and also limited to the Unintentional Injuries category, then the results show only those ICD codes that fall into the Unintentional Injuries group. The implicit relationship between these two data fields, ICD codes and Injury Intent, is observed when the query is processed. Until May 30, 2014, CDC WONDER only took these relationships into account for ontologically related hierarchical data, with clearly ordinate parent-child relationships, such as region/division/state/county and ICD chapter/sub-chapter/code. Now these implicit relationships are also taken into account when querying data with peer relationships, for the following data items:

  • Urbanization and County (each county is assigned an Urbanization category)
  • Injury Intent and specific Cause of Death as ICD Codes (each ICD Code is assigned an Injury Intent category)
  • Injury Mechanism and specific Cause of Death as ICD Codes (each ICD Code is assigned an Injury Mechanism category)
  • Drug / Alcohol Related Causes and specific Cause of Death as ICD Codes (each ICD Code is assigned a Drug / Alcohol category)
  • NCHS Rankable Causes of death (the 113 Causes List for all ages and the 130 Causes Lists for infants) and specific Cause of Death as ICD Codes (each ICD Code is assigned to a category in the NCHS Rankable Causes lists)

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What should I do when my request returns "too many rows" for the results?

Currently there is a cap on the potential number of rows available in the results to a query. This ceiling protects resources on the servers. Most queries results are limited to 75,000 rows of summary statistics. However, queries by individual records including narrative text fields are limited to 10,000 rows. The following approaches reduces the potential number of rows in the results:

  • Select fewer indexes or cross-tabulations for your results. These selections are made in the "Groups Results By..." lists in section 1 on the Request Form tab. Although 5-way tables are permitted for many databases, tables are easier to interpret and smaller with fewer indexes. The results to your query may include a row for each category in a data field selected as a "by-variable," such as more than three thousand counties in the nation, or more than nine thousand distinct causes of death classified by ICD-10 codes, or nearly sixteen thousand symptoms classified with Medical Dictionary for Regulatory Activities (MedDRA) concepts.
  • Limit the categories selected for the query. For example, you may wish to break out data by year, yet limit the years selected for each query to a range of 3 - 5 years, rather than all available years.
  • You may also wish run a series of related queries, export the results, and merge the various results sets. For example, run a query that groups results by demographic categories, yet limit each query to only one of the categories.
  • When running queries by County, you may wish to run separate queries for Georgia and Texas, due to the number of counties in these states.

If you wish to access the full data set, please click the "Other Data Access" link just below the tabs on the online database screens, to arrive at designated link to data provided by the respective data steward.

You may also contact CDC's Research Data Center with questions about analytic access to more detailed data from CDC.

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How do I get web pages, pictures and documents into a word processor on my PC?

To get a section from a web page:

Use your mouse to "click and drag" and highlight your desired selection from the page. Then "copy" the selection, move to your word processor with the target file open, place your cursor where the selection should go, and "paste" the selection. The "Copy" and "Paste" commands are usually found in your web browser's "Edit" menu at the top of the window, or found by clicking the right-hand mouse button. To select an image, such as a map or chart, then right click your mouse on the desired image. A menu pops open with options to capture and copy the image. Note that the map legends are separate image files. Your computer may also have "short-hand" key strokes for these commands.

To get the entire web page:

When a desired document is displayed in your browser, click on the "File" menu option at the top of the browser, then select "Save As." This action saves the web page to a file on your computer, and you can choose the file's name and location, and the file format. Later, you can "open" this file with your web browser or other software applications, such as a word processor. If your word processor cannot load web pages (HTML file format) then save the document as a text file.

Refer to the help feature for your computer's operating system, and for your specific desktop applications to learn more.

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What do I do when my browser fails to respond to commands or seems "stuck" loading a page?

Some large and complex data requests can take several minutes to process, and again take additional time and memory to download the results and display in your web browser. Please be patient with complex queries, and allow up to 10 minutes.

If your web browser is unable to load a page, then exit your browser and reopen it. If you cannot exit the web browser, try to end the process, for example by using the "Task Manager" for a "Windows" computer. If the problem still persists, exit all applications and shut down and then restart your system. Another application you are running may be conflicting with your browser.

We would appreciate it if you would inform us of any problems your browser has while using CDC WONDER. You can e-mail us at cwus@cdc.gov. Browser version and release information is displayed in your browser's "About" option under the "Help" menu.

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How do I resolve cache setting errors reported by my browser?

These problems can be resolved in your browser setup. You should contact your Internet Service Provider or search the help function of your browser. Here are some links to common browsers to help you expedite a resolution.

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Why do I get an error message when trying to connect to the Internet?

These types of messages usually result from trouble connecting to your Internet provider. You should contact your provider's technical support for assistance.

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What if my question isn't addressed here?

CDC WONDER is a product of Centers for Disease Control and Prevention. Questions or problems regarding this web site should be directed to cwus@cdc.gov.

This page last reviewed: Friday, June 17, 2022
This information is provided as technical reference material. Please contact us at cwus@cdc.gov.