In evaluating which reduced model for heritability and environmentality possessed the proper balance of parsimony and accuracy, the AIC and BIC differed in that the AIC indicated that a break point was needed at age 3. The BIC preferred model indicates that two linear slopes, one before age 15 and one after age 15, are required to accurately reflect the data, and we will focus on this model. Near birth, genetic influences account for nearly 70% of variation in personality and environmentality only accounts for 30% of variation. However, genetic effects decrease (b0–15 = −.013, p < .01) in magnitude while environmental effects increase (b0–15 = .013, p < .05) across early childhood. Following age 15, relatively small, but significant, changes occur in genetic (b15–90 = −.001, p < .05) and environmental (b15–90 = .002, p < .05) effects. This result is somewhat different when the environment is corrected for measurement unreliability. For example, the average effect size indicates that 31% of variation in personality associated with true environmental effects rather than 52%. The model that best reflects trends in
