We used a measurement model with 2 assessments to estimate the heritability of AD, while accounting for error of measurement, and also estimated the reliability of LTH-AD measured at each time point. Several noteworthy findings came out of fitting this model: First, as found in other studies examining AD in men, shared environmental influences were not statistically significant (Prescott and Kendler, 1999; Prescott et al., 1999; True et al., 1999). Second, when studying a single diagnostic assessment of LTH-AD in men, c. 23% of the variance in liability in fact reflects unreliability. Third, in the measurement model, forcing the factor loadings and error terms at times 1 and 2 to be equal did not significantly degrade the model-data fit. This suggests that the reliability at the first assessment, performed about 1 year earlier, was approximately the same as at the second assessment. Fourth, this series of models, to the best of our knowledge, provides the first estimates of “true” individual-specific etiology of LTH-AD in men. Moreover, we found that 51% of what would in a standard twin model be attributed
