We assessed the validity of our subsyndromal categories in two ways. First, we compared all the cross-disorder phenotypic correlations using the original dichotomous full-syndrome variables (tetrachoric correlations) with the three-category variables (polychoric correlations); 95% confidence intervals for these two correlations overlapped for 65 of 66 correlations. Second, using a multiple-threshold model in PRELIS 2.3 (36), we tested whether the three categories represented differing levels of severity on a single continuum of liability. This test failed at the 5% level three of 46 times, consistent with chance expectations (37).
