How many counties were covered by the survey in recent years? How many substate regions have data available?

NSDUH uses a stratified sampling design, with the United States divided into 750 sampling regions. While samples are taken from every region each year, many counties (especially sparsely populated counties) are not included in every year.

SAMHSA also uses small area estimation (SAE) methods, in which substate-level NSDUH data are combined with other data from smaller geographies to produce some indicators at the substate level. Some of these substate regions consist of a single county. There are approximately 400 substate regions across the United States. The definitions and maps of the regions are available on the SAMHSA website, along with the estimates for the regions.