title: Verifying the validity of outcome.
abstract: The first article in this series, published in May (page 241), dealt with selection bias and described how to tell if it had crept into  a clinical study. This article focuses on the next step in critically evaluating a study: How to assess validity of outcome. Examples illustrate the consequences of failure to fulfill each of the four criteria of valid measurement of outcome.
mesh_terms: D005260:Female; D006801:Humans; D010043:Outcome and Process Assessment, Health Care / Q000379:methods*; D011247:Pregnancy; D011446:Prospective Studies; D012107:Research Design; D012189:Retrospective Studies