Task 2: Key Concepts About Finding Datasets on the NHANES Website

 

Publicly-Released Datasets

Throughout the years, NHANES datasets and related information have been released in a variety of formats and different media. However, since the late 1990s, all publicly available data and related documentation are released and updated in a centralized location: the NHANES website.

The website contains the public-use data files for each of the NCHS national surveys starting with the first National Health Examination Survey (NHES I) dataset up to the most current dataset.  Datasets contain data for people who participate in a selected survey.  Currently, data files are released in 2-year increments, or cycles (e.g., NHANES 2003-2004).  The cycles since 1999 are referred to as “current NHANES” or “continuous NHANES.”  Codebooks and documentation are included with each of the data files. (For more information on locating data files and related documentation, see the Locate Variables module and the Download Data Files module.)

Several pages, described in more detail in the How To section of this task, will be particularly important for preparing and conducting analyses:

• Data Sets and Related Documentation,
• Survey cycle, and
• Data Documentation, Codebooks, SAS Code.

 

Data Sets and Related Documentation Page

The Data Sets and Related Documentation page lists all the survey cycles from the most recent to most historic.  It also provides the NHANES Analytic and Reporting Guidelines and the suggested citation for NHANES to use in publications.

 

Survey Cycle Page

The survey cycle page (titled by the survey cycle, e.g., NHANES 2003-2004) contains documentation about the survey, documentation on how to use the data, and links to:  

• Contents at a Glance, which has information about the survey in general terms
• Contents in Detail, which has detailed descriptions about the different items used in the survey including survey questionnaires, manuals, brochures and consent forms
• Using the Data, which has Analytic and Reporting Guidelines and documentation on how the data was released, and
• Data, Documentation, Codebooks, SAS Code, which has links to the five component pages:
  • Demographics
  • Dietary
  • Examination
  • Laboratory
  • Questionnaire

Component Page

The component page (titled by the survey cycle and then the component name, e.g., 2001-2002 Demographics) links to the data file and documentation for each component, as well as the variable list for each component.  For Continuous NHANES (starting in 1999), the data files, documentation, codebook and frequencies are available for every component. Starting with the 2003-2004 cycle, the codebook and frequencies were included in the documentation file.

Non-Publicly Released Datasets

NHANES uses the following principles to guide the release of data.  Data are to be released:

• as widely as practicable, 
• as soon as possible after data collection, and
• in as much detail as possible,
• while maintaining survey participant confidentiality.

As a result, some variables or entire data files are not publicly released due to disclosure concerns, for example, geographic identifiers. These files are only available through the Research Data Center (RDC). You may review the Data Release and Access Policy for more information.