Using all significant predictors of diagnostic reliability of LTH-AD, we created an index of caseness operationalized as a continuous measure of diagnostic confidence for all individuals assessed at time 1. Using cutoffs at increasing levels on this score, we calculated the heritability of LTH-AD at different levels of diagnostic confidence. For the 10 models fit according to this index, the best-fitting model included only additive genetics and individual-specific environmental factors. As depicted in Fig. 2, heritability of AD increased as diagnostic confidence increased (β = 1.22; R2 = 0.80; p < 0.01). At 3 lowest levels of diagnostic confidence, heritability of LTH-AD was estimated to be <10%, whereas at the highest level diagnostic confidence the heritability of LTH-AD was 82%.
