Assessing heterogeneity in meta-analysis: Q statistic or I² index?

Abstract

In meta-analysis, the usual way of assessing whether a set of single studies is homogeneous is by means of the Q test. However, the Q test only informs meta-analysts about the presence versus the absence of heterogeneity, but it does not report on the extent of such heterogeneity. Recently, the 12 index has been proposed to quantify the degree of heterogeneity in a meta-analysis. In this article, the performances of the Q test and the confidence interval around the 12 index are compared by means of a Monte Carlo simulation. The results show the utility of the 12 index as a complement to the Q test, although it has the same problems of power with a small number of studies.