We tested for change in heritability, shared environment, and non-shared environment estimates in Figure 3 by fixing relevant parameters to be equal at ages 17, 20, 24, and 29, testing for decrements in model fit. For example, to test for a change in heritability, we fixed the A component of each general factor to be equal, and tested the fit of this model against the original model where all A components are freely estimated. The decline in heritability noticed in Figure 3 was significant for males (χ2=23.86, df=3, p=2.7×10−5) and females (χ2=26.6, df=3, p=7.0×10−6). It appears thus that the vast majority of the phenotypic decline in Figure 3 is due to a decline in genetic variance. The increase in non-shared environment was also significant for males (χ2=15.73, df=3, p=.001) and females (χ2=11.48, df=3, p=.009). Changes in shared environment were not significant in either sex.
