Why are there differences in the 2021 estimates between the detailed tables released for 2021 and the detailed tables released for 2022?

The weights were adjusted for 2021 to make the estimates comparable to 2022 estimates.

When the NSDUH began including web responses along with in-person responses, it was determined that the mode of survey administration had an effect on the resulting estimates. In 2021, a smaller proportion of interviews were completed in person than in 2022, likely because of the COVID-19 pandemic. To account for mode differences between 2021 and 2022, estimates for 2021 were updated using adjusted weights.

The updated 2021 estimates used weights to set the contributions of respondents for each mode to the same proportions as the 2022 estimates, thus removing the potential for bias in estimates of change. See section 3.3.3 of the 2022 NSDUH Methodological Summary and Definitions for more details.

The 2021 detailed tables use the unadjusted estimates, while the 2022 detailed tables use the adjusted estimates to allow comparisons.