title: Defining successful treatment outcome in depression using the PHQ-9: a comparison of methods.
abstract: BACKGROUND
  Although the PHQ-9 is widely used in primary care, little is known about its performance in quantifying improvement. The original validation study of the PHQ-9 defined clinically significant change as a post-treatment score of ≤9 combined with improvement of 50%, but it is unclear how this relates to other theoretically informed methods of defining successful outcome. We compared a range of definitions of clinically significant change (original definition, asymptomatic criterion, reliable and clinically significant change criteria a, b and c) in a clinical trial of a community-level depression intervention.
  
  
  METHODS
  Randomised Control Trial of collaborative care for depression. Levels of agreement were calculated between the standard definition, other definitions, and gold-standard diagnostic interview.
  
  
  RESULTS
  The standard definition showed good agreement (kappa>0.60) with the other definitions and had moderate, though acceptable, agreement with the diagnostic interview (kappa=0.58). The standard definition corresponded closely to reliable and clinically significant change criterion c, the recommended method of quantifying improvement when clinical and non-clinical distributions overlap.
  
  
  CONCLUSIONS
  The absence of follow-up data meant that an asymptomatic criterion rather than remission or recovery criteria were used.
  
  
  CONCLUSIONS
  The close agreement between the standard definition and reliable and clinically significant change criterion c provides some support for the standard definition of improvement. However, it may be preferable to use a reliable change index rather than 50% improvement. Remission status, based on the asymptomatic range and a lower PHQ-9 score, may provide a useful additional category of clinical change.
authors.affiliation: Hull York Medical School and Department of Health Sciences, University of York, United Kingdom. dm645@york.ac.uk
authors.forename: Dean
authors.initials: D
authors.lastname: McMillan
authors.forename: Simon
authors.initials: S
authors.lastname: Gilbody
authors.forename: David
authors.initials: D
authors.lastname: Richards
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D019090:Case Management; D003299:Cooperative Behavior; D003865:Major Depressive Disorder / Q000175:diagnosis / Q000523:psychology / Q000628:therapy*; D005260:Female; D006801:Humans; D033183:Interdisciplinary Communication; D007406:Interview, Psychological; D008297:Male; D008875:Middle Aged; D010555:Personality Inventory / Q000706:statistics & numerical data*; D011320:Primary Health Care; D011594:Psychometrics / Q000706:statistics & numerical data; D015203:Reproducibility of Results; D006113:United Kingdom; D055815:Young Adult