The four-factor structure found in the NCS-A is also generally similar to findings from previous studies (Kessler et al., 2009b; Krueger, 1999; Vollebergh et al., 2001; Watson, 2005). Although a number of different specifications of the factor analysis model (e.g., at the person-level vs. person-year level, with and without sub-threshold bipolar disorder, with and without corrections for differential validity of diagnoses) yielded very similar results, replication in independent datasets is needed before considering this pattern stable.
