Classical behavioral genetic models use data collected from similarly aged siblings with varying degrees of genetic relatedness to decompose variation in a trait into that associated with genetic and environmental factors (Neale & Cardon, 1992). The typical behavioral genetic approach, for instance, uses data from monozygotic and dizygotic twins reared together and leverages the knowledge that monozygotic twins share nearly identical genetic material and dizygotic twins share approximately half of segregating genetic material on average. Genetic influences are then inferred to operate on a trait if monozygotic twins resemble one another more on that trait than dizygotic twins. Variance in the trait is decomposed into an additive genetic component (A), a shared environmental component (C), and a nonshared environmental component (E). The E component represents environmental influences that cause siblings to be less similar to one another and includes measurement error (which is by definition uncorrelated across siblings). The C component represents environmental experiences that cause siblings raised within the same home to be more similar to each other. However, a large body of literature indicates that personality traits are
