Fig. 1.

Variance component estimates for cognitive phenotypes based on meta-analysis of nonpsychiatric twin studies. Percentage variance explained by A (Additive genetic influences), C (Common environment), and E (Unique environment and Error) for individual test variables (plain font) and cognitive domains (bold font). Error bars and numbers in parentheses indicate 95% CIs. The sample size for a given cognitive domain differs from the summed sample size for test variables within that domain because inclusion criteria differ (supplementary methods).