title: Measurement invariance of the Depression Anxiety Stress Scales-21 across medical student genders.
abstract: OBJECTIVE
  This study aimed to assess whether male and female Iranian medical students perceived the meaning of the items in the Depression Anxiety Stress Scales-21 consistently.
  
  
  METHODS
  A convenience sample of 783 preclinical medical students from the first to sixth semester was invited to this cross-sectional study. Of the 477 respondents, 238 were male and 239 were female. All participants completed the Persian version of the Depression Anxiety Stress Scales-21. The graded response model was used to assess measurement invariance of the instrument across the gender groups. Categorical confirmatory factor analysis was used to evaluate the construct validity of the measure. Moreover, internal consistency was assessed via Cronbach's Alpha.
  
  
  RESULTS
  Statistically significant differential item functioning was flagged for just item 6 in the depression subscales (c2=6.5, df=1, p=0.011). However, removing or retaining the item 6 in the stress subscale did not change our findings significantly, when we compared stress scores across two genders. The results of categorical confirmatory factor analysis supported the fit of the three-factor model of Depression Anxiety Stress Scales-21. Moreover, Cronbach's alpha was greater than 0.7 in depression, anxiety and stress subscales.
  
  
  CONCLUSIONS
  This study revealed that Depression Anxiety Stress Scales-21 is an invariant measure across male and female medical students. Hence, this reliable and valid instrument can be used for meaningful comparison of distress scores between medical student genders. Gender comparisons of medical students' psychological profiles provide a better insight into gender influences on the outcome of medical education and medical practice.
authors.affiliation: Department of Biostatistics, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Peyman
authors.initials: P
authors.lastname: Jafari
authors.affiliation: Student Research Committee, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Farnoosh
authors.initials: F
authors.lastname: Nozari
authors.affiliation: Student Research Committee, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Forooghosadat
authors.initials: F
authors.lastname: Ahrari
authors.affiliation: Department of Biostatistics, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Zahra
authors.initials: Z
authors.lastname: Bagheri
mesh_terms: D001007:Anxiety / Q000175:diagnosis* / Q000453:epidemiology; D003430:Cross-Sectional Studies; D003863:Depression / Q000175:diagnosis* / Q000453:epidemiology; D005163:Factor Analysis, Statistical; D005260:Female; D006801:Humans; D007492:Iran; D008297:Male; D011569:Psychiatric Status Rating Scales; D015203:Reproducibility of Results; D012737:Sex Factors; D013315:Stress, Psychological / Q000175:diagnosis* / Q000453:epidemiology; D013337:Students, Medical / Q000523:psychology*
keywords: dass-21; iran; measurement invariance; medical students