Key Concepts About Identifying NHANES III Variable Names and File Locations

Variables are stored in different data files. Data files are organized by their collection method, which can fall under one of four components: Examination, Laboratory, Questionnaire (for Adults and Youths, as well as demographics) and Foods, and by release date, which is typically subject specific. Usually analyses will require more than one component. For instance age and gender are in the demographics component of the Adult or Youth Questionnaire, while blood pressure measurements are in the Examination component, cholesterol variables are in the Laboratory component, and questions about previous diagnoses or taking medications for hypertension are also in the Adult Questionnaire component. All these variables would be required in a complete analysis of cardiovascular disease.

Data for different components of the survey are released in separate data files to facilitate a more timely data release and faster access over the Internet. Below is a list of the basic file types in NHANES III  Series 11, No. 1A, July 1997-Interview & Exam Components and a summary of their contents.  NHANES III Series 11, No. 2A,
April 1998-Electrocardiogram, Dietary Recall, Laboratory, Dietary Supplement and Prescription Drug includes updates to some of these file types plus additional data releases.  Subsequent releases which are subject specific are self-explanatory.

• Examination files: information collected through physical exams and dental exams and mobile examination center (MEC) interview. (Note: not every survey participant agreed to a physical examination)
• Laboratory files: results from analyses of blood and urine
• Questionnaire files: data collected through household interview, plus survey design (e.g. weights, design strata) and demographic variables
• Foods:  information collected on dietary recall and other dietary interview components over a period of time.

The component's documentation contains a Data File Index  listing  

• variable's English label (a short description of the variable)
• variable name, and
• position of the variable (NHANES III was originally released on mainframe data tapes; the variable position refers to the data tape position)

Use the Adobe search feature (binoculars) to locate " Data File Index" .  Once at the Data File Index section of the documentation, use the search feature again to locate the variables of interest.  Not every result returned will be relevant to your analysis. The data file documentation (discussed in the next task) will guide you to the appropriate variables for your analysis.

For example, there are two sets of cholesterol variables — from the General Biochemistry Tests and the Biochemistry Profile. You have identified the variable names (TCP and CHP), so now you can consult the data file documentation to learn which variables to use in your analysis.

All variables listed in the documentation have been publicly released and are available for download in the associated data file. If you wish to use a variable that is not listed in a component variable list, you will need to use the Research Data Center. You can review the Research Data Center for more information about how to obtain access to non-publicly released variables