FIGURE 1.
Bivariate biometric dual change score model to examine genetic and environmental influences on the relationship between age changes in two measures: G (general cognitive ability) and T (temperament factor). Error variance (σu) is assumed to be constant at each age within each factor; αG and αT represent constant change related to the slope factors Gs and Ts; βG and βT represent proportional change in G and T; cross-trait coupling is indicated by λG and λT. The model includes estimates for intercepts (G0 and T0), mean intercepts (μG0 and μT0), and mean slopes (μGs and μTs). The model includes genetic effects specific to each intercept (aG0 and aT0) and specific to each slope (aGs and aTs). The paths from aG0 to Gs and from aT0 to Ts generate the decomposition of the correlation between the intercept and slope for G and T. Note that shared environmental (cG0, cT0, cGs, and cTs) and nonshared environmental (eG0, eT0, eGs, and eTs) parameters were also included in the model but are not included in the figure