Second, estimates of shared environmental effects can be biased upward by assortative mating for AUDs. This is because when spouses have correlated liabilities for AUD, the correlation between the genetic factors of DZ twins and siblings would be higher than 0.5, which is assumed in the model. The spousal correlation for AUD was estimated at equal to +0.12 as found in one prior large-scale general population study (Maes et al. 1998). If this spousal resemblance results entirely from assortative mating (spouses choosing one another, directly or indirectly, on the basis of their genetic risk for AUD) rather than spousal interaction (spouses mutually influencing each other's drinking and hence liability to AUD), then inflation of the shared environmental variance component would be ~0.06, a little over half of the estimated shared environmental variance component from the meta-analysis. Accordingly, some proportion of our estimate of shared environmental effects for AUD may be a result of assortative mating.
