Monitoring Depression Treatment Outcomes With the Patient Health Questionnaire-9

Although effective treatment of depressed patients requires regular follow-up contacts and symptom monitoring, an efficient method for assessing treatment outcome is lacking. We investigated responsiveness to treatment, reproducibility, and minimal clinically important difference of the Patient Health Questionnaire-9 (PHQ-9), a standard instrument for diagnosing depression in primary care.

This study included 434 intervention subjects from the IMPACT study, a multisite treatment trial of late-life depression (63% female, mean age 71 years). Changes in PHQ-9 scores over the course of time were evaluated with respect to change scores of the SCL-20 depression scale as well as 2 independent structured diagnostic interviews for depression during a 6-month period. Test-retest reliability and minimal clinically important difference were assessed in 2 subgroups of patients who completed the PHQ-9 twice exactly 7 days apart.