Psychometric properties of the 21-item Depression, Anxiety, and Stress Scale (DASS-21) among Malaysians during COVID-19: a methodological study.

Depression, anxiety, and stress continue to be among the largest burdens of disease, globally. The Depression, Anxiety, and Stress Scale-21 Items (DASS-21) is a shortened version of DASS-41 developed to measure these mental health conditions. The DASS-41 has strong evidence of validity and reliability in multiple contexts. However, the DASS-21, and the resulting item properties, has been explored less in terms of modern test theories. One such theory is Item Response Theory (IRT), and we use IRT models to explore latent item and person traits of each DASS-21 sub-scale among people living in Malaysia. Specifically, we aimed to assess Classical Test Theory and IRT properties including dimensionality, internal consistency (reliability), and item-level properties. We conducted a web-based cross-sectional study and sent link-based questionnaires to people aged 18 and above in a private university and requested to roll out the link. Overall and individual sub-scales' Cronbach's alpha of the DASS-21 indicates an excellent internal consistency. The average inter-item correlation and corrected inter-item correlations for each of the sub-scales indicated acceptable discrimination. On average, DASS-21 total scores and sub-scale scores were significantly higher among female participants than males. The Graded Response Model had better empirical fit to sub-scale response data. Raw summated and latent (IRT estimated) scores of the Depression, Anxiety, and Stress sub-scales, and overall DASS-21 were strongly correlated. Thus, this study provides evidence of validity supporting the use of the DASS-21 as a mental health screening tool among Malaysians. Specifically, standard error of measurement was minimized to provide robust evidence of potential utility in identifying participants who are and are not experiencing these mental health issues. Additional research is warranted to ensure that test content culturally appropriate and accurately measuring cultural norms of depression, anxiety, and stress.