Sometimes you may wish to analyze only a certain demographic subgroup of interest, such as a particular age range or gender, or whether survey participants were tested for a particular lab analyte or other examination criteria.
For SUDAAN procedures it is important that you do not create a smaller subgroup based on any non weight-related groups of interest (e.g. demographic, laboratory or examination variables) in the SAS data step before executing the SUDAAN procedure. Instead, it is highly recommended that you create a subset of your sample population using the subpopn statement in the SUDAAN procedure itself and not in the SAS data step. In addition, SUDAAN procedures require that all observations in the dataset being read into a procedure have the same sample weight. Therefore, prior to the SUDAAN procedure you should create a subset of your data to include only those observations with the appropriate sample weight for your analysis.
For SAS Survey procedures, there is no subpopn statement. Instead, most SAS 9.2 Survey procedures use a domain statement for domain analysis, also known as subgroup analysis or subpopulation analysis. In SAS 9.1 Survey Procedures, proc surveymeans, proc surveyreg, proc surveyfreq, and proc surveylogistic have different methods for selecting a subpopulation.
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