How Can We Use Depression Severity to Guide Treatment Selection when Measures of Depression Categorize Patients Differently?

Objective: Treatment guidelines for depression suggest that severity should be taken into account when initiating treatment. If clinicians are to consider illness severity in selecting among treatment options for depression, then it is important to have reliable, valid, and clinically useful methods of distinguishing between levels of depression severity. In the present report from the Rhode Island Methods to Improve Diagnostic Assessment and Services (MIDAS) project, we compared 3 self-report scales that assess the DSM-IV criteria for major depressive disorder on the basis of how these scales distribute patients into severity categories.

Method: From June 2010 to November 2011, 245 depressed outpatients completed the Clinically Useful Depression Outcome Scale (CUDOS), Quick Inventory of Depressive Symptomatology (QIDS), and Patient Health Questionnaire (PHQ-9). The study was conducted at Rhode Island Hospital, Providence, Rhode Island. The patients were subdivided into severity categories according to the cutoff scores recommended by each scales' developers. The patients were also rated on the 17-item Hamilton Depression Rating Scale (HDRS-17).

Results: The correlations between the HDRS-17 and the 3 self-report scales were nearly identical. Yet the scales significantly differed in their distribution of patients into severity categories. On the CUDOS and HDRS-17, moderate depression was the most frequent severity category, whereas on the PHQ-9 and QIDS, the majority of the patients were classified as severe. Significantly fewer patients were classified as severely depressed on the CUDOS compared to the PHQ-9 (McNemar = 153.8; P < .001) and QIDS (McNemar = 114.0; P < .001).

Conclusions: If clinicians are to follow treatment guidelines' recommendations to base initial treatment selection on the severity of depression, then it is important to have a consistent method of determining depression severity. The marked disparity between standardized scales in the classification of depressed outpatients into severity groups indicates that there is a problem with the use of such instruments to classify depression severity. Caution is warranted in the use of these scales to guide treatment selection until the thresholds to define severity ranges have been empirically established.