Cross-Sectional Retrospective Assessments versus Longitudinal Prospective Assessments of Substance Use Change among Young Adults during COVID-19: Magnitude and Correlates of Discordant Findings.

: Findings regarding changes in substance use since COVID-19 have been mixed, potentially due to differences in methods used to assess change. Thus, we compared changes in substance use per retrospective self-report at one time-point (March-May 2020) versus prospective, longitudinal self-report across 2 time-points (Sept-Dec 2019; March-May 2020), and identified predictors of discordance. We analyzed data from a longitudinal study of 1,082 young adults from 6 metropolitan areas. Across cigarettes, e-cigarettes, marijuana, and alcohol, participants were categorized as Increasers (increased based on both methods), Decreasers/Stable (decreased/same per both methods), Over-reporters (decreased/same per longitudinal data/increased via retrospective report), or Under-reporters (increased per longitudinal data/decreased/same via retrospective report). We identified predictors (e.g., sociodemographics, pre-pandemic substance use levels) of Under-reporting. In this sample (M24.77; 45.7% male, 32.1% sexual minority, 4.0% Black, 12.4% Asian, 12.6% Hispanic), longitudinal data indicated that the proportions of cigarette, e-cigarette, marijuana, and alcohol users who increased their use were 43.3%, 41.7%, 52.6%, and 55.6%, respectively. Examining concordance/discordance groups, Under-reporters accounted for between 17.7% (alcohol) and 26.8% (e-cigarette) of users; over-reporters comprised among the smallest proportions of each group (17.4% for alcohol to 22.2% for marijuana). Multivariable regression indicated that predictors of Under-reporting were less pre-pandemic use across substances; being older for e-cigarettes; and being older, male, and Asian for alcohol. Findings highlight methodological variability as a potential reason for mixed findings regarding pandemic-related substance use change and underscore the need for rigorously designed research to accurately assess the population impact of COVID-19 and other historical events.