When the process of publication favors studies with smallp-values, and hence large effect estimates, combined estimates from many studies may be biased. This paper describes a model for estimation of effect size when there is selection based on one-tailedp-values. The model employs the method of maximum likelihood in the context of a mixed (fixed and random) effects general linear model for effect sizes. It offers a test for the presence of publication bias, and corrected estimates of the parameters of the linear model for effect magnitude. The model is illustrated using a well-known data set on the benefits of psychotherapy.
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Authors' note: The contributions of the authors are considered equal, and the order of authorship was chosen to be reverse-alphabetical.
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Vevea, J.L., Hedges, L.V. A general linear model for estimating effect size in the presence of publication bias. Psychometrika 60, 419–435 (1995). https://doi.org/10.1007/BF02294384
- research synthesis
- publication bias
- effect size
- mixed models
- selection models