title: Evaluating heterogeneity in cumulative meta-analyses.
abstract: BACKGROUND
  Recently developed measures such as I2 and H allow the evaluation of the impact of heterogeneity in conventional meta-analyses. There has been no examination of the development of heterogeneity in the context of a cumulative meta-analysis.
  
  
  METHODS
  Cumulative meta-analyses of five smoking cessation interventions (clonidine, nicotine replacement therapy using gum and patch, physician advice and acupuncture) were used to calculate I2 and H. These values were plotted by year of publication, control event rate and sample size to trace the development of heterogeneity over these covariates.
  
  
  RESULTS
  The cumulative evaluation of heterogeneity varied according to the measure of heterogeneity used and the basis of cumulation. Plots produced from the calculations revealed areas of heterogeneity useful in the consideration of potential sources for further study.
  
  
  CONCLUSIONS
  The examination of heterogeneity in conjunction with summary effect estimates in a cumulative meta-analysis offered valuable insight into the evolution of variation. Such information is not available in the context of conventional meta-analysis and has the potential to lead to the development of a richer picture of the effectiveness of interventions.
authors.affiliation: Monash Institute of Health Services Research, Monash University, Clayton, Victoria, Australia. Elmer.Villanueva@nbcc.org.au
authors.forename: Elmer V
authors.initials: EV
authors.lastname: Villanueva
authors.forename: Silva
authors.initials: S
authors.lastname: Zavarsek
mesh_terms: D026881:Acupuncture; D003000:Clonidine / Q000627:therapeutic use; D003376:Counseling; D003627:Data Interpretation, Statistical; D015987:Effect Modifier, Epidemiologic; D006801:Humans; D015201:Meta-Analysis as Topic; D009538:Nicotine / Q000627:therapeutic use; D016017:Odds Ratio; D016032:Randomized Controlled Trials as Topic / Q000706:statistics & numerical data; D012307:Risk Factors; D016540:Smoking Cessation / Q000379:methods / Q000706:statistics & numerical data*; D014029:Tobacco Use Disorder / Q000453:epidemiology* / Q000628:therapy*
chemical_list: D009538:Nicotine; D003000:Clonidine