We tested for measurement invariance of the symptom counts across sex by fitting multiple group confirmatory factor analysis models within cohort. Results indicated that the loadings and thresholds could not be equated across sex for any of the symptom counts in Cohort II or Cohort III (Cohort II: p=.004-p<.0001, Cohort III: p=.002-p<.0001). Follow-up tests for evidence of differential item functioning (DIF) were conducted using MIMIC models (Jöreskog & Goldberger, 1975) and items within all three symptom counts showed evidence of DIF. Complete results of these tests are available in Tables S1–S3 in supplemental materials. Results of tests for DIF were used to inform the multivariate model-fitting (see Results).
