
What is a metaanalysis?
A metaanalysis is a quantitative approach to reviewing research literature in a specific area. In educational research, the many factors that vary from one teaching context to another make it difficult to design definitive experiments to determine if a given instructional approach affects a given student outcome. A metaanalysis combines a number of studies (usually conducted by a number of different researchers in a variety of educational contexts) to quantify the effect a given instructional approach has on a given outcome. By broadening the pool of data to include many different contexts (and increasing sample sizes) a better quantitative estimate can be made of how much a given instructional practice affects students.
Technical details on conducting metaanalyses can be found in the literature (Glass, et al., 1981; Hedges, et al., 1985; Cooper, 1989), though the process usually includes these steps:
 Independent variables (e.g., cooperative learning as a teaching and learning method) and outcome variables (e.g., academic achievement) of interest are clarified.
 Quantitative research that addresses the independent and outcome variables of interest is identified.
 Quantitative information from each study that indicates the effect the independent variable has on the outcome variable is determined.
 The data are "normalized" by determining the effect size for the data reported in the study. The effect size is the difference between the means of the outcome scores of the experimental and control groups divided by the standard deviation of the scores. A positive effect of the instructional strategy on the outcome variable is indicated by a mean effect size across the studies that is greater than 0.
Glass, G. V., McGaw, B., & Smith, M. L. Metaanalysis in Social Research. Sage: Beverly Hills, CA, 1981.
Hedges, L. V., and Olkin, I. Statistical Methods for MetaAnalysis.
Academic Press: Orlando, FL, 1985.
Cooper, H. M. Integrating Research: A Guide for Literature Reviews. (2nd
ed.). Sage: Newbury Park, CA, 1989.
