In the next step, we used a co-relative design utilizing same-sex cousin, half-sibling, full-sibling, and monozygotic twin pairs. We identified unique combinations of pairs and used conditional Cox regression, where each pair is treated as a stratum, meaning the effect of the covariates are estimated within each pair, thereby controlling for confounding factors shared within that pair. Neither of the members of the pair was registered for alcohol use disorder or was married before age 18. Marital status is included as a time-dependent covariate; either one member of the pair met our criteria for marriage over the follow-up period and one did not, or they were married at different ages.
