title: A case study of pooled-studies publications indicated potential for both valuable information and bias.
abstract: OBJECTIVE
  Pooled-studies publications (PSPs) present statistical analyses of multiple randomized controlled trials without a systematic literature search or critical appraisal. We explored the characteristics of PSPs and their potential impact on a systematic review (SR).
  
  
  METHODS
  We systematically evaluated PSPs excluded from an SR of second-generation antidepressants. We analyzed their basic characteristics, risk of bias, and the effect of new data on review conclusions.
  
  
  RESULTS
  We identified 57 PSPs containing a median of five trials (range, 2-11) and 1,233 patients (range, 117-2,919). Ninety-six percent of PSPs were industry funded, and 49% of PSPs contained unpublished data. The median number of citations for PSPs was 29 (range, 0-549). Only 7% planned pooling a priori, and 19% combined trials with identical protocols. Fifty-nine percent of PSPs eligible for general efficacy provided no new data. For some subgroups and accompanying symptoms (e.g., anxiety, insomnia, melancholia, fatigue, sex, and race), more than 30% of PSPs presented entirely new data or data that could alter the strength of the evidence available in the SR.
  
  
  CONCLUSIONS
  In this case study, PSPs provided new information on subgroups and secondary outcomes; however, guidance for reviewers and development of a system to assess their susceptibility to bias are required.
authors.affiliation: Department for Evidence-based Medicine and Clinical Epidemiology, Danube University Krems, 3500 Krems, Austria. kylie.thaler@donau-uni.ac.at
authors.forename: Kylie J
authors.initials: KJ
authors.lastname: Thaler
authors.forename: Laura C
authors.initials: LC
authors.lastname: Morgan
authors.forename: Megan
authors.initials: M
authors.lastname: Van Noord
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Jonas
authors.forename: Marian S
authors.initials: MS
authors.lastname: McDonagh
authors.forename: Kimberly
authors.initials: K
authors.lastname: Peterson
authors.forename: Anna
authors.initials: A
authors.lastname: Glechner
authors.forename: Gerald
authors.initials: G
authors.lastname: Gartlehner
mesh_terms: D000928:Antidepressive Agents / Q000627:therapeutic use; D003627:Data Interpretation, Statistical; D006801:Humans; D017594:Publication Bias; D011643:Publishing; D016032:Randomized Controlled Trials as Topic; D012196:Review Literature as Topic
chemical_list: D000928:Antidepressive Agents
keywords: Antidepressants; Bias; Depression; Pooling; Subgroups; Systematic review