Beyond the forest plot: The drapery plot
Gerta Rücker, Guido Schwarzer
Abstract
In the era of the "reproducibility crisis" and the "P-value controversy" new ways of presentation and interpretation of the results of a meta-analysis are desirable. One suggestion that has been made for single studies almost six decades ago and taken up now and then is the P-value function. For a given outcome, this function assigns a P-value to each possible hypothetical value, given the data. Moreover, the P-value function simultaneously provides two-sided confidence intervals for all possible alpha levels. An application to meta-analysis, while suggested early, has not been widely established. We introduce the drapery plot that presents the P-value function for all individual studies and pooled estimates in a meta-analysis as curves and the prediction range for a single future study. We also present a scaled variant with the test statistic on the y-axis. Both plots visualize the full information of a pairwise meta-analysis. We see a drapery plot as a complementary figure to a forest plot. It may be even an alternative in meta-analyses with many studies where forest plots tend to become very large and complex.