How should I handle the degrees of freedom when conducting hypothesis testing with NHANES data?
Unlike with simple random samples, you cannot simply use n-1 as the degrees of freedom in NHANES since it is a multi-stage, area probability sample. So the number of independent pieces of information, or degrees of freedom, depends upon the number of PSUs rather than on the number of sample persons. Therefore, the degrees of freedom are calculated as the number of first stage units (PSUs) containing observations minus the number of strata (please see Sample Design module for more information).
