Table 1.

Prevalence of and associations between covariates used in the study and lifetime and early cannabis use (<17 years of age) and nonsuicidal self-injury (NSSI) in 9,583 male and female Australian twins

Variable	Prevalence %	Association with cannabis use, unadjusted OR [95% CI]	Associationa with early cannabis use, unadjusted OR [95% CI]	Association with NSSI, unadjusted OR [95% CI]
Lifetime cannabis use	62.8	–
Early-onset cannabis use	28.6	–	–
NSSI	5.1	2.84 [2.23, 3.61]	2.15 [1.75, 2.65]	–
Depressed mood	6.8	1.16 [0.98, 1.37]	1.35 [1.09, 1.66]	5.67 [4.52, 7.11]
Social anxiety	8.3	1.19 [1.02, 1.39]	3.86 [3.09, 4.83]	1.20 [0.98, 1.46]
Regular smoking	11.0	2.61 [2.22, 3.06]	1.43 [1.22, 1.68]	2.17 [1.71, 2.75]
Regular alcohol use	13.4	3.41 [2.91, 4.00]	2.41 [2.10, 2.77]	1.65 [1.30, 2.08]
Illicit drug use	3.8	4.91 [3.55, 6.79]	4.84 [3.83, 6.11]	4.36 [3.29, 5.79]
Conduct disorder	9.7	4.58 [3.72, 5.63]	2.76 [2.37, 3.22]	3.38 [2.72, 4.19]
Childhood sexual abuse	7.7	1.90 [1.59, 2.28]	1.42 [1.18, 1.71]	3.64 [2.88, 4.60]

Notes: The prevalence rates for all covariates account for time-varying effects, such that the age at onset had to occur before age 17 (threshold for early cannabis use) both for those who reported ever using cannabis and for lifetime non-users. Among those reporting cannabis use, the covariate was only considered present if occurring before the onset of cannabis use. OR = odds ratio; CI = confidence interval.

^aORs in this column are based on a subsample of 6,009 lifetime cannabis users.