A case study of pooled-studies publications indicated potential for both valuable information and bias

J Clin Epidemiol. 2013 Oct;66(10):1082-92. doi: 10.1016/j.jclinepi.2013.05.002. Epub 2013 Jul 10.


Objectives: 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).

Study design and setting: 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 Ninety-six percent of PSPs were industry funded, and 49% of PSPs contained unpublished data.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.

Conclusion: 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.

Keywords: Antidepressants; Bias; Depression; Pooling; Subgroups; Systematic review.

Publication types

  • Review
  • Systematic Review

MeSH terms

  • Antidepressive Agents / therapeutic use
  • Data Interpretation, Statistical
  • Humans
  • Publication Bias
  • Publishing*
  • Randomized Controlled Trials as Topic*
  • Review Literature as Topic*


  • Antidepressive Agents