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 I² 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 I² index are compared by means of a Monte Carlo simulation. The results show the utility of the I² index as a complement to the Q test, although it has the same problems of power with a small number of studies.
Huedo-Medina, Tania; Sanchez-Meca, Julio; Marin-Martinez, Fulgencio; and Botella, Juan, "Assessing heterogeneity in meta-analysis: Q statistic or I2 index?" (2006). CHIP Documents. 19.
Reprinted from Psychological Assessment, Vol.11, Issue 2, June 2006, pp. 193-206 'This article may not exactly replicate the final version published in the APA journal. It is not the copy of record.' Homepage for journal Psychological Assessment: http://www.apa.org/journals/pas/