As shown in table 1, both in identical and in fraternal twins the coefficients for the genetic effects are identical to the coefficients for the GxSE interaction effects, indicating that both types of effects are confounded. In other words, the genetic variances estimated in twin studies will include the effects of GxSE interaction effects.7 One approach to separate the genetic and GxE interaction effects—the study of children of twins—is discussed in the next section.
