Defining successful treatment outcome in depression using the PHQ-9: a comparison of methods

J Affect Disord. 2010 Dec;127(1-3):122-9. doi: 10.1016/j.jad.2010.04.030. Epub 2010 May 31.


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.

Method: 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.

Limitations: The absence of follow-up data meant that an asymptomatic criterion rather than remission or recovery criteria were used.

Conclusion: 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.

Publication types

  • Comparative Study
  • Multicenter Study
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Case Management*
  • Cooperative Behavior*
  • Depressive Disorder, Major / diagnosis
  • Depressive Disorder, Major / psychology
  • Depressive Disorder, Major / therapy*
  • Female
  • Humans
  • Interdisciplinary Communication*
  • Interview, Psychological
  • Male
  • Middle Aged
  • Personality Inventory / statistics & numerical data*
  • Primary Health Care*
  • Psychometrics / statistics & numerical data
  • Reproducibility of Results
  • United Kingdom
  • Young Adult