What weights should I use in IHIS?
NHIS data are collected through a complex stratified sampling scheme that includes oversampling of some population subgroups. This means that persons and households with some characteristics are over-represented in the samples, while others are underrepresented. To obtain representative statistics using IHIS data, users must apply weights.
IHIS contains several weights. Which weight to use depends on the unit of analysis (household or person) and the sampling approach for the variable(s) in question (e.g., all persons versus a sample adult or sample child drawn from each family).
Each variable description contains a tab specifying the weight that should be used with that variable in each year, if that variable were analyzed in isolation. If multiple variables using different sampling strategies and weights are combined in one table or in a multivariate analysis, then the weight employed should fit the variable with the most restrictive sampling scheme. For example, the variables AGE and SEX apply to all persons, and therefore take the weight PERWEIGHT, while ASTHMAEV (ever told had asthma) was collected for sample persons only and takes the weight SAMPWEIGHT. To make a table of ASTHMAEV by AGE, controlling for SEX (using either downloaded data or the online tabulator), users should apply SAMPWEIGHT, which matches ASTHMAEV, the variable with the most restrictive sampling scheme.
For more information about the use of weights with IHIS data, consult the User Note on Weights.