A note on testing for homogeneity among effect sizes sharing a common control group.
L. V. Hedges and I. Olkin (1985) presented a statistic to test for homogeneity among correlated effect sizes and L. J. Gleser and I. Olkin (1994) presented a large-sample approximation to the covariance matrix of the correlated effect sizes. This article presents a more exact expression for this covariance matrix, assuming normally distributed data but not large samples, for the situation where effect sizes are correlated because a single control group was compared with more than one treatment group. After the correlation between effect sizes has been estimated, the standard Q statistic for correlated effect sizes can be used to test for homogeneity. This method is illustrated using results from schizophrenia research.
Cook
Samantha R
SR
Harvard University, Cambridge, MA, USA. cook@stat.columbia.edu
D006801:Humans; D008960:Models, Psychological; D017063:Outcome Assessment, Health Care / Q000706:statistics & numerical data*; D011584:Psychology / Q000379:methods* / Q000706:statistics & numerical data; D012559:Schizophrenia / Q000628:therapy