Periodicity and severity of changes in depression and anxiety during the COVID-19 pandemic: Ten-wave longitudinal findings from an observational cohort study of community adults.

AIMS: Few multi-wave longitudinal studies have examined mental health changes across the coronavirus 2019 (COVID-19) pandemic. The current study examined: (a) overall changes in depression and anxiety over 10-waves of data collection; (b) subgroup moderators of changes; (c) clinical severity of the changes via minimally important differences (MIDs); and (d) correlates of clinically important changes. METHODS: Using a longitudinal observational cohort design, 1412 non-clinical adults (Mage=36; 60% female) were assessed for depression and anxiety via the PHQ-9 and GAD-7 from October 2018 to April 2022 (3 pre-pandemic, 7 intra-pandemic waves; M retention = 92%). RESULTS: Depression and anxiety exhibited significant intra-pandemic changes, reflecting initial increases, followed by decreases. Pre-pandemic severity moderated changes, with low severity participants exhibiting increases and high severity participants exhibiting non-significant change or decreases. For depression and anxiety, respectively, 10% and 11% exhibited MID increases, while 4% and 6% exhibited MID decreases. Divergent patterns were present by severity subgroup, with the lowest severity exhibiting higher rates of MID increases and the highest severity subgroup exhibiting higher rates of MID decreases. CONCLUSIONS: These findings illuminate the periodicity of depression and anxiety during the COVID-19 pandemic and reveal an unexpected inverse relationship between increases and decreases based on pre-pandemic severity.