Estimating the causal effect of conduct disorder on the time from first substance use to substance use disorders using g-estimation.

BACKGROUND: The effect of conduct disorder (CD) as a major risk factor of substance use disorder (SUD), controlling for other psychiatric problems, has been well established in the literature. However, other psychiatric problems are associated as confounders with an increased risk of SUD. When confounding exists, the use of the standard survival analysis approach would lead to a biased estimate of the effect of a time-varying exposure on the time to event. METHODS: The authors used a G-estimation approach to estimate the causal effect of CD while controlling for time-varying confounders. RESULTS: The present study (N = 1420) found a substantial difference in the estimated hazard ratio of CD (4.49 vs. 1.93) when the results from G-estimation and Cox regression were compared. CONCLUSIONS: G-estimation fixed the problem of underestimating the hazard ratio of conduct disorder (CD) while controlling for all measured covariates.