Figure 1.

Wald tests produced by the sandwich corrected ULS procedure compared with the test statistic obtained based on full information maximum-likelihood (standard ML) estimation method. We simulated 1000 datasets consisting of 500 MZ and 500 DZ four-sib families, and we varied the effect size of the genetic effect (1%, 0.25% and the null model). The heritability of the trait was h²=70%. The dots above the diagonal show the number of times the standard ML procedure produced a larger test statistic.