Meta-analysis is a statistical method to summarize the different individual studies under the same subject。 InR and Hedges'd are the two effect sizes that are most commonly used in ecology.They are compared in analyzing response of plant ecophysilogical variables to high CO₂ concentration.For the same variable, two effect size might result in different overall effect size and even occasionally change its direction.LnR was apt to lead to positive effect.The range of overall effect sizes of 24 variables given by Hedges'd was wider than that by InR.Effect size given by LnR was asymmetry, while that by Hedges'd symmetry.