title: Monitoring depression treatment outcomes with the patient health questionnaire-9.
abstract: BACKGROUND
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  The PHQ-9 responsiveness as measured by effect size was significantly greater than the SCL-20 at 3 months (-1.3 versus -0.9) and equivalent at 6 months (-1.3 versus -1.2). With respect to structured diagnostic interviews, both the PHQ-9 and the SCL-20 change scores accurately discriminated patients with persistent major depression, partial remission, and full remission. Test-retest reliability of the PHQ-9 was excellent, and its minimal clinically important difference for individual change, estimated as 2 standard errors of measurement, was 5 points on the 0 to 27 point PHQ-9 scale.
  
  
  CONCLUSIONS
  Well-validated as a diagnostic measure, the PHQ-9 has now proven to be a responsive and reliable measure of depression treatment outcomes. Its responsiveness to treatment coupled with its brevity makes the PHQ-9 an attractive tool for gauging response to treatment in individual patient care as well as in clinical research.
authors.affiliation: Department of General Internal and Psychosomatic Medicine, Heidelberg University Medical Center, D-69120 Heidelberg, Germany. bernd.loewe@med.uni-heidelberg.de
authors.forename: Bernd
authors.initials: B
authors.lastname: Löwe
authors.forename: Jürgen
authors.initials: J
authors.lastname: Unützer
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Callahan
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Perkins
authors.forename: Kurt
authors.initials: K
authors.lastname: Kroenke
mesh_terms: D000368:Aged; D003865:Major Depressive Disorder / Q000175:diagnosis / Q000628:therapy*; D039721:Diagnostic and Statistical Manual of Mental Disorders; D019263:Dysthymic Disorder / Q000175:diagnosis / Q000628:therapy*; D005260:Female; D006801:Humans; D007406:Interview, Psychological; D008297:Male; D017063:Outcome Assessment, Health Care / Q000379:methods*; D011320:Primary Health Care / Q000592:standards*; D011569:Psychiatric Status Rating Scales; D011594:Psychometrics / Q000295:instrumentation*; D011788:Quality of Life / Q000523:psychology; D020377:Self Efficacy; D018434:Sickness Impact Profile; D011795:Surveys and Questionnaires