Why does SAMHSA caution against comparing 2020 estimates with estimates from other years?

Because of the coronavirus disease 2019 (COVID-19) pandemic, major changes were made to the methods used in data collection in 2020. There is no way to separate out the true changes in behavior from the changes due to the new methodology.

The main methodological changes were:

• Almost no data collection from mid-March through September 2020,
• Introduction of web data collection in October 2020 with very limited in-person data collection, and
• Additions to the questionnaire beginning in October 2020.

The 2020 NSDUH is missing two quarters of data. Tests of data from before 2020 show that estimates based on just quarters 1 and 4 are not comparable to estimates based on the entire year. This indicates that 2020 estimates should not be compared to previous years. Repeated analyses have showed that web responses are not comparable to in-person responses, and that the comparability is not consistent in a way that we can fully account for. For these reasons, it is not recommended to compare any estimates from 2020 to estimates from other survey years.

A full description of the analyses that were conducted can be found in chapter 6 of the 2021 Methodological Summary and Definitions report.