Fig. 1.

Estimates of parental shared environment $\left(\widehat{\xi }\right)$. Results for NHS (a) and HPFS (b) under simulation models, where the heritability of type 2 diabetes (σ_G1² + σ_G2²) is 0.40, σ_G1²=0.03, σ_E1²=0.18, σ_G2² =0.37, σ_E2² =0.42 and x=0.0, 0.4, 0.5 or 0.6. The best estimate (or fit) of ξ for a dataset $\left(\widehat{\xi }\right)$ is the value of ξ that minimizes the sum of squared residuals based on differences between observed variances in analyses of real phenotypes and the fitted variances in analyses of simulated phenotypes (see Materials and methods).