Charting the landscape of graphical displays for meta-analysis and systematic reviews: a comprehensive review, taxonomy, and feature analysis

Abstract

Background: Data-visualization methods are essential to explore and communicate meta-analytic data and results. With a large number of novel graphs proposed quite recently, a comprehensive, up-to-date overview of available graphing options for meta-analysis is unavailable. Methods: We applied a multi-tiered search strategy to find the meta-analytic graphs proposed and introduced so far. We checked more than 150 retrievable textbooks on research synthesis methodology cover to cover, six different software programs regularly used for meta-analysis, and the entire content of two leading journals on research synthesis. In addition, we conducted Google Scholar and Google image searches and cited-reference searches of prior reviews of the topic. Retrieved graphs were categorized into a taxonomy encompassing 11 main classes, evaluated according to 24 graph-functionality features, and individually presented and described with explanatory vignettes. Results: We ascertained more than 200 different graphs and graph variants used to visualize meta-analytic data. One half of these have accrued within the past 10 years alone. The most prevalent classes were graphs for network meta-analysis (45 displays), graphs showing combined effect(s) only (26), funnel plot-like displays (24), displays showing more than one outcome per study (19), robustness, outlier and influence diagnostics (15), study selection and p-value based displays (15), and forest plot-like displays (14). The majority of graphs (130, 62.5%) possessed a unique combination of graph features. Conclusions: The rich and diverse set of available meta-analytic graphs offers a variety of options to display many different aspects of meta-analyses. This comprehensive overview of available graphs allows researchers to make better-informed decisions on which graphs suit their needs and therefore facilitates using the meta-analytic tool kit of graphs to its full potential. It also constitutes a roadmap for a goal-driven development of further graphical displays for research synthesis.

Beyond the forest plot: The drapery plot

“…Thompson suggested a very similar plot based on a completely different consideration in the framework of Fuzzy Set Theory, called “fuzzy number plot,” 26 see also Kossmeier et al 27 Here, the y‐axis represents the “membership grade,” in this framework meaning the grade (between 0 and 1) to which an element belongs to a (fuzzy) set. Grade 1 means that the fuzzy set reduces to a one‐point interval of length 0, here the observed point estimate.…”

The orchard plot: Cultivating a forest plot for use in ecology, evolution, and beyond

“…A formal definition of the term "caterpillar plot" seems to be missing in the literature, but it appears to have been used when a forest plot (1) excludes the overall mean (often depicted by a diamond; as for a confidence interval plot 39 ) and/or (2) has individual effect sizes ordered from the smallest to the largest (eg, Reference 40 ). Here, we use the term caterpillar plot to refer to the latter.…”

More than words: Novel visualizations for evidence synthesis

“…The explosion of developments in meta‐analytic methodology over the last decades has been accompanied by a respective explosion of visualization methods for presenting those developments. Thus, apart from the forest plot and the funnel plot, a large array of visualization methods has been proposed in the literature since 1978 7 …”