Other psychological outcomes have also yielded significant evidence of gene-environment interaction effects in the twin literature. For example, a moderating effect, parallel to that reported for alcohol consumption above, has been reported for depression symptoms (Heath et al. 1998) in females. A marriage-like relationship reduced the influence of genetic liability to depression symptoms, paralleling the effect found for alcohol consumption: Genetic factors accounted for 29% of the variance in depression scores among married women, but for 42% of the variance in young unmarried females and 51% of the variance in older unmarried females (Heath et al. 1998). Life events were also found to moderate the impact of factors influencing depression in females (Kendler et al. 1991). Genetic and/or shared environmental influ-ences were significantly more important in influencing depression in high-stress than in low-stress environments, as defined by a median split on a life-event inventory, although there was insufficient power to determine whether the moderating influence was on genetic or environmental effects.
