title: Assessment of regression-based methods to adjust for publication bias through a comprehensive simulation study.
abstract: BACKGROUND
  In meta-analysis, the presence of funnel plot asymmetry is attributed to publication or other small-study effects, which causes larger effects to be observed in the smaller studies. This issue potentially mean inappropriate conclusions are drawn from a meta-analysis. If meta-analysis is to be used to inform decision-making, a reliable way to adjust pooled estimates for potential funnel plot asymmetry is required.
  
  
  METHODS
  A comprehensive simulation study is presented to assess the performance of different adjustment methods including the novel application of several regression-based methods (which are commonly applied to detect publication bias rather than adjust for it) and the popular Trim & Fill algorithm. Meta-analyses with binary outcomes, analysed on the log odds ratio scale, were simulated by considering scenarios with and without i) publication bias and; ii) heterogeneity. Publication bias was induced through two underlying mechanisms assuming the probability of publication depends on i) the study effect size; or ii) the p-value.
  
  
  RESULTS
  The performance of all methods tended to worsen as unexplained heterogeneity increased and the number of studies in the meta-analysis decreased. Applying the methods conditional on an initial test for the presence of funnel plot asymmetry generally provided poorer performance than the unconditional use of the adjustment method. Several of the regression based methods consistently outperformed the Trim & Fill estimators.
  
  
  CONCLUSIONS
  Regression-based adjustments for publication bias and other small study effects are easy to conduct and outperformed more established methods over a wide range of simulation scenarios.
authors.affiliation: Department of Health Sciences, University of Leicester, Leicester, UK. sgm8@le.ac.uk
authors.forename: Santiago G
authors.initials: SG
authors.lastname: Moreno
authors.forename: Alex J
authors.initials: AJ
authors.lastname: Sutton
authors.forename: A E
authors.initials: AE
authors.lastname: Ades
authors.forename: Tom D
authors.initials: TD
authors.lastname: Stanley
authors.forename: Keith R
authors.initials: KR
authors.lastname: Abrams
authors.forename: Jaime L
authors.initials: JL
authors.lastname: Peters
authors.forename: Nicola J
authors.initials: NJ
authors.lastname: Cooper
mesh_terms: D003198:Computer Simulation; D006801:Humans; D015201:Meta-Analysis as Topic; D016017:Odds Ratio; D017594:Publication Bias; D016032:Randomized Controlled Trials as Topic; D012044:Regression Analysis