Shared environmental influences are most prominent during the first two epochs, accounting for 24–29% of the total variance. After this, their influence declines to 4% of the variance by epoch 6. Unique environmental factors also decline in significance over time, though less dramatically: in epoch 1, they account for 76% of the variance; 64% during epoch 2; and 43–55% from epochs 3–6. Factor loadings from E1–E3 are primarily time-specific, with little influence on later epochs; however, even these low cross-time loadings differ significantly from 0 (Fig. 1, Appendix Table A2). Beginning with E4, which loads first onto epoch 4 (ages 22–25 years), unique environmental factors are modestly influential over time rather than being nearly completely occasion-specific.
