Contour-Enhanced Funnel Plots for Meta-Analysis

Abstract

Funnel plots are commonly used to investigate publication and related biases in meta-analysis. Although asymmetry in the appearance of a funnel plot is often interpreted as being caused by publication bias, in reality the asymmetry could be due to other factors that cause systematic differences in the results of large and small studies, for example, confounding factors such as differential study quality. Funnel plots can be enhanced by adding contours of statistical significance to aid in interpreting the funnel plot. If studies appear to be missing in areas of low statistical significance, then it is possible that the asymmetry is due to publication bias. If studies appear to be missing in areas of high statistical significance, then publication bias is a less likely cause of the funnel asymmetry. It is proposed that this enhancement to funnel plots should be used routinely for meta-analyses where it is possible that results could be suppressed on the basis of their statistical significance.

Comparative outcome of PFNA, Gamma nails, PCCP, Medoff plate, LISS and dynamic hip screws for fixation in elderly trochanteric fractures: a systematic review and network meta-analysis of randomized controlled trials

“…Meta-regression was applied to explore the source of heterogeneity [e.g., mean age, percentage of females, body mass index (BMI), follow-up time and ASA status] if data were available. Publication bias was assessed using contour-enhanced funnel plots [18,20] and Egger tests [3].…”

Is unicompartmental knee arthroplasty (UKA) superior to total knee arthroplasty (TKA)? A systematic review and meta-analysis of randomized controlled trial

“…Subgroup or sensitivity analysis was then performed according to the results of meta-regression. Publication bias was assessed using contour funnel plots [21,22] and Egger tests [8]. Asymmetry of the funnel plot might be due to missing data in some studies, in which the results that were negative might not have been published and thus could not be identified.…”

Comparative efficacy of pharmacological and non-pharmacological interventions in fibromyalgia syndrome: network meta-analysis

“…For primary outcomes we drew funnel plots of trials comparing any active intervention with non-intervention or placebo controls,33 enhanced by contours dividing the plots into areas of significance and non-significance at a two-sided p=0.05,34 35 and added lines of predicted treatment effects derived from univariable random effects meta-regression models using the standard error as explanatory variable 36 37. Funnel plot asymmetry was assessed with Egger's test 38…”