Symptoms of Major Depressive Disorder Scale: Performance of a Novel Patient-Reported Symptom Measure

Highlights

• The Symptoms of Major Depressive Disorder Scale (SMDDS) was developed in accordance with the recommendations and scientific best practices set forth in the Food and Drug Administration's guidance for industry and recent scientific literature for achieving content validity of patient-reported outcome measures.

• This observational study of 315 adults with major depressive disorder (MDD) provides the quantitative evidence supporting the measurement properties of the SMDDS.

• The SMDDS can reliably and validly assess patient-reported MDD symptoms and has been qualified by the Food and Drug Administration for exploratory use in MDD treatment trials.

Abstract

Background

The Symptoms of Major Depressive Disorder Scale (SMDDS) was expressly developed on the basis of qualitative data to directly incorporate patients' voices into evaluation of treatment benefit in major depressive disorder (MDD) clinical trials.

Objectives

To collect quantitative data necessary to refine/optimize the SMDDS and document its psychometric properties.

Methods

In this multicenter, observational study, participants with clinically diagnosed MDD completed questionnaires in 2 waves. Wave 1 was designed to refine the SMDDS using Rasch measurement evaluations and item reduction analyses. On a subset of wave 1 subjects, 7 to 12 months later, wave 2 further examined item performance and measurement properties. Exploratory factor analyses and assessments of construct validity and reliability (internal consistency and reproducibility) were completed.

Results

Using wave 1 data (N = 315; females = 71%, white = 81%, mean age = 44 years), the SMDDS was revised from 36 to 16 items. The Rasch item threshold map indicated that all but 1 item (suicidal ideation) were appropriately ordered. The 207 wave 2 participants were 74% females, 82% white, with a mean age of 45 years. The exploratory factor analyses resulted in a single component (all standardized factor loadings >0.46). Cronbach α was 0.93 and the 7-day test-retest intraclass correlation coefficient (n = 93) was 0.84 (95% confidence interval 0.77-0.89). SMDDS scores discriminated between MDD severity levels.

Conclusions

The 16-item SMDDS generated highly reliable scores with substantial evidence of construct validity. On the basis of the evidence of appropriate content validity and sound psychometric performance, the Food and Drug Administration qualified the SMDDS as an outcome measure to support exploratory efficacy endpoints in MDD clinical trials.