A previous NCS-A report documented high lifetime prevalence of disorders (Merikangas et al., 2010). Overall prevalence is even higher in the current data because we included sub-threshold bipolar disorder, which was omitted from the earlier report. (Table 1) Comorbidity is also more common because we analyze hierarchy-free diagnoses, with 27.9% of respondents meeting criteria for two or more disorders and a mean of 3.5 disorders among those with comorbidity. All but two of the 105 tetrachoric correlations among disorder pairs (15×14/2) are positive (82.5% statistically significant), with a median of .29 and inter-quartile range (25th-75th percentiles) of .20-.37. (The tetrachoric correlation matrix is available on request.)
