title: Primary study authors of significant studies are more likely to believe that a strong association exists in a heterogeneous meta-analysis compared with methodologists.
abstract: OBJECTIVE
  To assess the interpretation of a highly heterogeneous meta-analysis by authors of primary studies and by methodologists.
  
  
  METHODS
  We surveyed the authors of studies on the association between insulin-like growth factor 1 (IGF-1) and prostate cancer, and 20 meta-analysis methodologists. Authors and methodologists presented with the respective meta-analysis results were queried about the effect size and potential causality of the association. We evaluated whether author responses correlated with the number of IGF-related articles they had published and their study results included in the meta-analysis. We also compared authors' and methodologists' responses.
  
  
  RESULTS
  Authors who had published more IGF-related papers offered more generous effect size estimates for the association (ρ(s)=0.61, P=0.01) and higher likelihood that the odds ratio (OR) was greater than 1.20 (ρ(s)=0.63, P=0.01). Authors who had published themselves studies with statistically significant effects for a positive association were more likely to believe that the true OR is greater than 1.20 compared with methodologists (median likelihood 50% versus 2.5%, P=0.01).
  
  
  CONCLUSIONS
  Researchers are influenced by their own investment in the field, when interpreting a meta-analysis that includes their own study. Authors who published significant results are more likely to believe that a strong association exists compared with methodologists.
authors.affiliation: Department of Hygiene and Epidemiology, Clinical and Molecular Epidemiology Unit and Clinical Trials and Evidence-Based Medicine Unit, University of Ioannina School of Medicine, Ioannina 45110, Greece.
authors.forename: Orestis A
authors.initials: OA
authors.lastname: Panagiotou
authors.forename: John P A
authors.initials: JP
authors.lastname: Ioannidis
mesh_terms: D000465:Algorithms; D015415:Biomarkers / Q000097:blood; D019538:Health Care Surveys; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008297:Male; D015201:Meta-Analysis as Topic; D016017:Odds Ratio; D011471:Prostatic Neoplasms / Q000097:blood / Q000378:metabolism*; D012107:Research Design
chemical_list: D015415:Biomarkers; D007334:Insulin-Like Growth Factor I