Univariate genetic model-fitting: model fit and parameter estimates (95% confidence intervals in parentheses).

Note. −2LL = twice the negative log-likelihood, the difference between −2LL of two models is subjected to chi-square (χ2) distribution. Two fit indices are reported: change in chi-square (Δχ2) and Bayesian Information Criterion (BIC). Δdf = change in degrees of freedom (df). a2, c2, and e2 are proportion of variance due to additive genetic (A), shared environmental (C) and non-shared environmental effect (E). E, CE, and AE models are nested within ACE; the best fitting model is underlined.