power of quasi-causal designs comes from comparison of sibling pairs who are discordant on a factor of interest. Under a causal model, if the risk factor has a causal impact on the phenotype, the exposed sibling would have a higher rate of conduct disorder compared to the non-exposed sibling. Under a non-causal model, where the risk factor is confounded by familial factors (genetic or environmental), the exposed sibling and the unexposed sibling would show similar rates of conduct disorder. Accordingly, genetically informed designs can give important insights about the risk factors to prioritize in prevention and intervention efforts.
