title: Empirical assessment of effect of publication bias on meta-analyses.
abstract: OBJECTIVE
  To assess the effect of publication bias on the results and conclusions of systematic reviews and meta-analyses.
  
  
  METHODS
  Analysis of published meta-analyses by trim and fill method.
  
  
  METHODS
  48 reviews in Cochrane Database of Systematic Reviews that considered a binary endpoint and contained 10 or more individual studies.
  
  
  METHODS
  Number of reviews with missing studies and effect on conclusions of meta-analyses.
  
  
  RESULTS
  The trim and fill fixed effects analysis method estimated that 26 (54%) of reviews had missing studies and in 10 the number missing was significant. The corresponding figures with a random effects model were 23 (48%) and eight. In four cases, statistical inferences regarding the effect of the intervention were changed after the overall estimate for publication bias was adjusted for.
  
  
  CONCLUSIONS
  Publication or related biases were common within the sample of meta-analyses assessed. In most cases these biases did not affect the conclusions. Nevertheless, researchers should check routinely whether conclusions of systematic reviews are robust to possible non-random selection mechanisms.
authors.affiliation: Department of Epidemiology and Public Health, University of Leicester, Leicester LE1 6TP.
authors.forename: A J
authors.initials: AJ
authors.lastname: Sutton
authors.forename: S J
authors.initials: SJ
authors.lastname: Duval
authors.forename: R L
authors.initials: RL
authors.lastname: Tweedie
authors.forename: K R
authors.initials: KR
authors.lastname: Abrams
authors.forename: D R
authors.initials: DR
authors.lastname: Jones
mesh_terms: D002986:Clinical Trials as Topic; D006801:Humans; D015201:Meta-Analysis as Topic; D017594:Publication Bias; D015203:Reproducibility of Results