Measurement invariance of the Depression Anxiety Stress Scales-21 across medical student genders

Objectives 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.