Identify the sampling method as simple random sampling, systematic, convenience sampling, or stratified sampling.
An IRS (Internal Revenue Service) auditor randomly selects for audits 80 taxpayers in each of the filing status categories: single, head of household, married filing jointly, and married filing separately.
We use this method when we are concerned about differences among subgroups, or strata, within a population. We first identify the subgroups and then draw a simple random sample within each subgroup. The total sample consists of all the samples from the individual subgroups.