EXTFUNNEL: Stata module to produce graphical augmentations to the funnel plot to indicate the potential impact of a new study on an existing meta-analysis

extfunnel creates graphical overlay augmentations to the funnel plot. The purpose of these overlays is to display the potential impact a new study would have on an existing meta-analysis, providing an indication of the robustness of the meta-analysis to the addition of new evidence. Thus, these extend the use of the funnel plot beyond assessments of publication biases. Two main graphical displays can be produced; i) statistical significance contours, which define regions of the funnel plot in which a new study would have to be located in order to change the statistical significance of the meta-analysis; and ii) heterogeneity contours, which show how a new study would affect the extent of heterogeneity in a given meta-analysis. extfunnel can also illustrate the impact a new study has on lower and upper confidence interval values, the confidence interval width of the pooled meta-analytic result, and overlays for the impact of a future study on, user defined, limits of clinical equivalence. Inverse variance weighted methods are implemented using both explicit formulae for contour lines, and a simulation approach optimised in Mata.