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)

Average Discrete Change^b

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)

Female

Male

Female

Male

Female

Male

Estimated Causal Effect^b

(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