Validity and severity thresholds for the depression subscale of the affective self rating scale: An equipercentile equating study using classical test theory

•The affective self rating scale (ASRS) measures depressive and manic symptoms.•The ASRS depression subscale was validated with the PHQ-9 and QIDS-16 in a university clinic setting.•Proposed thresholds for affective self rating scale (ASRS) are 5, 11, 16 and 23.•Exploratory factor analysis of ASRS, PHQ-9 and QIDS-16 provided construct validity Background: The Affective Symptoms Scale (ASRS) is a unique instrument designed to separately measure depressive and manic symptoms in mood disorders. We validated the ASRS against the Patient Health Questionnaire (PHQ-9) and the Quick Inventory of Depressive Symptomatology (QIDS-16). Methods: A retrospective study of 258 patients who completed the PHQ-9, QIDS-16 and ASRS as part of routine clinical care. To establish meaningful clinical thresholds for the depression subscale of the ASRS, it was equated with the QIDS and the PHQ-9. Results: The depression subscale of the ASRS had significant positive correlations with the QIDS-16 and the PHQ-9 (respectively, r= 0.8, t[253] = 19.8, p < 0.001, and r= 0.8, t[245] = 28.2, p < 0.001). The equipercentile equating method with the PHQ-9 indicated that the thresholds corresponded to ASRS depression subscale scores of 5.4, 10.6, 16.1, and 23. Equating with the QIDS indicated that thresholds corresponded to ASRS depression subscale scores of 5.1, 11, 18.4, and 27.5. Limitations: Limitations include a small sample size that did not allow more detailed statistical analysis, such as Item Response Theory. The population is a heterogenous population at a university outpatient setting. Conclusions: The ASRS depression subscale significantly correlated with the PHQ-9 and QIDS-16. Our proposed threshold scores for the ASRS are 5, 11, 16 and 23 to indicated mild, moderate, severe and very severe depression respectively.