Some general points in estimating heterogeneity variance with the DerSimonian.Laird estimator

In this paper we consider estimating heterogeneity variance with the DerSimonian.Laird (DSL) estimator as typically used in meta.analysis.In its general form the DSL estimator requires inverse population.averaged study.specific variances as weights, in which case the estimator is unbiased.It has become common practice, however, to use estimates of the study.specific variances instead of their population.averaged versions.This can lead to considerable bias.Simulations illustrate these findings.