 the paper proposes a new measure called diversity, d2, to estimate the relative variance reduction when changing from a random effects to a fixed effects model meta-analysis. d2 is calculated as the percentage of between trial variability that contributes to the sum of between trial variability and a sampling error estimate considering the required information size. The authors show that d2 is greater than or equal to the commonly used measure of heterogeneity, inconsistency, i2, for all meta-analyses. They also demonstrate mathematically that d2 can be used to adjust the required information size in any random effects model meta-analysis. The paper suggests that d2 is a better alternative to i2 when considering model variation in random effects meta-analyses. This article was authored by Glad Christian, Brock Jesper, Thorland Christian, and others. We are article.tv, links in the description below.