To illustrate the effect of attenuation on heritability estimates, 101 datasets were generated consisting of 400 MZ twin pairs and 600 DZ twin pairs. A standard normally distributed latent trait was simulated with an additive genetic component of 72% and a non-shared environmental component of 28%. The 1PL IRT model was used to simulate responses to 14 dichotomous items, where the β parameter values ranged from 0.5 to 3.5, with increments of 0.25. This corresponds to questionnaire items that are rarely endorsed by people. The simulated item data were fitted using a model with additive genetic and non-shared environmental effects (AE model) on a latent trait and a 1PL measurement model.
