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Two issues that complicate behavioral genetic analyses are the interaction and correlation between genetic and environmental influences. In this report, the effects of genotype-envi ronment interaction and correlation on behavioral genetic studies (twin and adoption studies) are examined. The analysis suggests that genotype-environment interaction may bias twin study estimates of genetic and environmental influence, but need not affect adoption studies. On the other hand, genotype-environment correlation may affect both twin and adoption study estimates of genetic and environmental influence, the direction of the effect depending on the sign of the correlation. Finally, new tests of genotypeenvironment interaction and correlation, using adoption data, are proposed.
Plomin et al. (Sat,) studied this question.