To identify predictors of reliably diagnosed LTH-AD, we used logistic regression. Beginning with the 1,040 male subjects who met the DSM-IV criteria for LTH-AD at time 1, we examined the ability of clinical features of AD assessed at time 1 to predict consistent reporting of an LTH-AD at time 2. As there was a period of at least 1 year between the 2 assessments, any new cases that occurred during this period were excluded from the analysis. This was performed to ensure that the reporting of LTH-AD symptom criteria spanned the same lifetime period at both interviews. In the stepwise logistic regression analyses, using SPSS 17 (SPSS for Windows [Computer program], 2008), we applied a p-value of 0.05 for variables to be entered into analyses and 0.10 for them to be excluded. Due to dependence within twin pairs, we ran the solution found in the stepwise procedure again using Mplus 5.2 (Muthén and Muthén, 2007) using the “complex sample” feature to obtain correct standard errors.
