Figure 4.

Parameter estimates ± 1 SE for the contributions to variation in liability to psychoactive drug use of additive genetic effects (a²), familial environmental factors (c²), and the individual-specific environment (e²) by year for the average daily number of caffeine-containing drinks for ages 9 to 35 years (A), the average daily number of cigarettes for ages 13 to 35 years (B), the average number of alcoholic drinks consumed per month for ages 14 to 40 years (C), and the average number of units of cannabis consumed per month for ages 14 to 35 years (D). The actual parameter estimates are depicted by the black lines, and the colored regions represent the possible range of estimates ± 1 SE.