Variables are stored in different data files. Data files are organized into 20 topic areas and by whether the data were collected on the original NHANES I sample or the detailed subsample. Usually analyses will require more than one component. For instance age and sex are in the demographics component of all the data tapes, while blood pressure measurements are in the Medical Examination Ages 1-74 years component, the cholesterol measurement is in the Biochemistry, Serology, Hematology, Blood Slides, Urine Dipst.(ick) component, and questions about previous diagnoses or taking medications for hypertension are in the Medical History Questionnaire, Ages 12-74 years 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 focused analytic option for researchers and faster access over the Internet. Below is a list of the basic files in NHANES I Data Files, Documentation, Codebook 1971-75, as reviewed in the Data Structure and Contents module. The titles indicate the topic area contents.
The component's documentation contains a Demographic Data Summary common to all the files. It also contains a [File Title] Data Summary specific to that file, which lists the
Use the Adobe search feature ("find" box on bottom toolbar or binoculars button on top toolbar) to locate "Data Summary." Once at the Data Summary 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 hypertension history variables — from the Medical History Questionnaire, Ages 12-74 years file and the Health Care Needs, General Medical History Supplement, and Respiratory and Cardiovascular Supplements, Ages 25-74 years file. You have identified the variable names (N1AH0290 and N1AH0423 versus N1GM0548 / N1GM0549 and N1GM0560), 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.