Objective: Several common methods for measuring treatment response present a snapshot of depression symptoms. The construct of estimated depression-free days (DFDs) simultaneously captures treatment outcome and estimates the patient's experience of depression over time. The study compared this measure with traditional measures used in depression treatment research.
Methods: This secondary data analysis was based on data from the Improving Mood-Promoting Access to Collaborative Treatment trial, a multisite depression treatment study conducted in 18 primary care clinics in five states and representing eight health care systems. The sample of older adults (N=906) had been randomly assigned to receive collaborative care for depression. Participants were aged 60 or older and met criteria for major depressive disorder, dysthymia, or both. Exclusion criteria included severe cognitive impairment, active substance abuse, active suicidal behavior, severe mental illness, and active treatment from a psychiatrist. The Patient Health Questionnaire (PHQ-9) and the Hopkins Symptom Checklist (HSCL-20) were used as outcome measures at four assessment points (baseline, three months, six months, and 12 months). Outcomes were computed for relative change, standardized differences, the proportion of improvement in depression, and DFDs.
Results: Using four assessment points improved the agreement between DFDs and the course of symptom change between pre- and posttest measures.
Conclusions: The DFD is a valid measure for estimating treatment outcomes that reflects the course of symptom change over time. When multiple assessments were conducted between the pre- and posttest periods, DFDs incorporated additional data yet remained easily interpreted. The DFD should be considered for reporting outcomes in depression research.