How to quantify between-study heterogeneity in single-arm evidence synthesis?—It depends!

Although different heterogeneity variance estimators produce substantially different heterogeneity variance estimates, too little attention is paid to selecting a suitable heterogeneity variance estimator in single-arm evidence synthesis. Based on our literature review, we conclude that the awareness of different heterogeneity variance estimators and their properties needs to be strengthened in practice. Given that it is rarely appropriate to rely on a single heterogeneity variance estimator, we suggest careful consideration and evaluation of a wider range of plausible estimators in a sensitivity analysis before drawing a final conclusion about the meta-analysis results.