Reliability and validity of depression anxiety stress scale (DASS)-21 in screening for common mental disorders among postpartum women in Malawi

Background Approximately one in five women who have recently given birth suffer from common mental disorder (CMD), particularly depression and/or anxiety. Most available CMD screening tools in most low- and middle-income countries do not screen for more than one mental health problem. Having a screening tool that is free to use, short in assessment time, and used to screen for more than one CMD is appealing in a resource-constrained setting. Method We conducted a criterion validation study of the Chichewa translated and adapted DASS-21 instrument against gold standard diagnoses of depression and anxiety disorders using an independently administered Structured Clinical Interview for DSM-IV (SCID). We compared the performance of the DASS-depression subscale with the Edinburgh Postpartum Depression Scale (EPDS). Internal reliability was reported using both Cronbach’s alpha and ordinal alpha. The DASS-21 and EPDS ability to discriminate cases from non-cases was assessed by receiver operating characteristics (ROC) analysis. We selected cut-off points for DASS-21 and EPDS that maximise both sensitivity and specificity. Results One hundred fifteen participants were administered all the measures. Approximately 11.3% and 14.8% had depression and anxiety diagnoses respectively using SCID. The overall Cronbach’s alpha for the DASS-21 scale was 0.74. The DASS-21 subscales had Cronbach’s alpha values of 0.66, 0.29 and 0.52 for depression (DASS-D), anxiety (DASS-A) and stress (DASS-S), respectively. The ordinal alpha for DASS-D, DASS-A and DASS-S subscales were 0.83, 0.74 and 0.87, respectively. The area under the ROC curve was 0.76 (95% CI: 0.61; 0.91) for DASS-D and 0.65 for DASS-A. At a cut-off point of one or more, the sensitivity and specificity for DASS-D were 69.2% and 75.5%, whilst DASS-A was 52.9% and 75.5%, respectively. Pearson correlation coefficient for the association between DASS-D and EPDS was r = 0.61, p < 0.001. Conclusion The DASS-21 had good internal reliability (Cronbach’s alpha), and its ordinal alpha demonstrated good internal reliability for all its sub-scales. Regarding the criterion validation, only the DASS-D and EPDS demonstrated a satisfactory ability to discriminate cases from non-cases. Our findings suggest that health practitioners can use DASS-D as an alternative tool in screening depression as it has fewer questions than EPDS.