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Table 2 Average discrete change of cannabis use indicators over survey waves, and estimated causal effect of COVID-19 on cannabis use by difference-in-difference, stratified by sex, among eligible students attending the 43 linked-longitudinal COMPASS schools across the three study waves (2018, 2019, 2020)

From: Examining the impact of the early stages of the COVID-19 pandemic period on youth cannabis use: adjusted annual changes between the pre-COVID and initial COVID-lockdown waves of the COMPASS study

  Cannabis Use
Monthly Usea Weekly Usea Daily Usea
  Difference Mean (95% CI) Difference Mean (95% CI) Difference Mean (95% CI)
  Female Male Female Male Female Male
Average Discrete Changeb 2019–2018 (pre-COVID-19 period) 5.0 (0.4, 0.6) 7.9 (6.4,9.4) 2.9 (1.2, 4.5) 5.2 (3.7, 6.8) 0.5 (0.1, 1.0) 1.2 (0.5, 1.8)
2020–2019 (early COVID-19 period) 0.2 (−0.3, 0.3) 1.1 (− 0.9, 3.0) 0.9 (−1.7, 3.5) 1.1 (− 1.9, 4.1) 1.3 (0.5, 2.0) − 0.4 (−1.4, 0.5)
  Difference-in-Difference
(95% CI)
Difference-in-Difference
(95% CI)
Difference-in-Difference
(95% CI)
Female Male Female Male Female Male
Estimated Causal Effectb (2020-2019) – (2019-2018) −4.8 (−8.2, −1.4)
p = 0.006
−6.8 (− 9.7, −3.9)
p < 0.001
−2.0 (−5.9, 2.0)
p = 0.325
−4.1 (− 8.2, −0.1)
p = 0.045
0.8 (−0.2, 1.7)
p = 0.138
−1.6 (− 2.9, − 0.3)
p = 0.016
  1. Notes: 95% CI (confidence interval)
  2. a Fixed effect model with a lagged variable as the outcome, controlling for time-invariant confounders but constraining sex and age effects on the outcome to be fixed across time, and sample selection correction with the predictors of age, weekly spending money, school connectedness, and province.
  3. b based on adjusted estimates.