Indices of model fit to assess within-group genetic and environmental contributions and between-group racial heterogeneity.

The table presents the following values: −2 times the log likelihood (-2LL), the number of free parameters in the model (k), an index of the balance between goodness of model fit and parsimony (Akaike's information criterion, or AIC), and the p-value significance result from the likelihood ratio test (distributed as a chi-square statistic). The fit of model 2 was compared to model 1 and all subsequent models were compared to model 2. Significant p-values indicate a significant reduction in model fit. AA = African American, EA = European American, f2 = fetal effect, m2 = maternal effect and c2 = shared environmental effect.