Meta-analysis: Recent developments in quantitative methods for literature reviews

We describe the history and current status of the meta-analytic enterprise. The advantages and historical criticisms of meta-analysis are described, a s are the basic steps in a meta-analysis and the role of effect sizes as ch ief coins of the meta-analytic realm. Advantages of the meta-analytic proce dures include seeing the "landscape" of a research domain, keeping statisti cal significance in perspective, minimizing wasted data, becoming intimate with the data summarized, asking focused research questions, and finding mo derator variables. Much of the criticism of metaanalysis has been based on simple misunderstanding of how meta-analyses are actually carried out. Crit icisms of meta-analysis that are applicable are equally applicable to tradi tional, nonquantitative, narrative reviews of the literature. Much of the r emainder of the chapter deals with the processes of effect size estimation, the understanding of the heterogeneity of the obtained effect sizes, and t he practical and scientific importance of the effect sizes obtained.