of youth age across calendar years revealed that we had substantial numbers of qualifying prepandemic assessments of 11-year-olds in the years 2018/2019 and of 12-year-olds in the year 2019. Thus, the age-period design consisted of comparing the prevalence of substance use among 11-year-olds in 2020 (during pandemic) versus 2018/2019 (before pandemic) and among 12-year-olds in 2020 (during pandemic) versus 2019 (before pandemic). There were no meaningful differences in the sociodemographic composition of 11- or 12-year-old youth in each of these calendar years after applying inverse probability weights (Table S5).
