Analysing the simulated item data with a 1PL IRT model, using the one-step approach, we recovered the true 72% value for the heritability coefficient closely (see Table 1). When analysing the raw sum scores using a normal AE model, either with or without transformation, the heritability point estimate dropped considerably, to about 42%. Thus, when the true model is an IRT model and the number of items is limited, an analysis of raw or transformed sum scores can lead to extensive underestimation of heritability. Table 1Simulation results. Reported heritability values are the medians of the 101 posterior means and medians, standard deviations between parenthesesMethod of analysisHeritability coefficient point estimatesPosterior meanPosterior median1PL IRT model0.7232 (0.0585)0.7245 (0.0589)Sum scores continuous model0.4364 (0.0393)0.4369 (0.0395)Log-transformed sum scores0.4046 (0.0403)0.4047 (0.0406)
