Comparability
The values of SMLKSNOW changed in 2015, when the "rarely" category was eliminated and the set of possible response values was reduced to "every day," "some days," or "not at all." Aside from this coding change, comparability may be affected by a major questionnaire redesign introduced in 2019.
The NHIS questionnaire was substantially redesigned in 2019 to introduce a different data collection structure and new content. For more information on changes in terminology, universes, and data collection methods beginning in 2019, please see the user note.
