This Digest provides a review and applications of the concepts of normal distribution, standard deviation, effect size, and translation of effect size into percentile gain, the foundations for the understanding of meta analytic results. Meta analysis is a statistical technique that enables the results of a number of studies to be combined to determine the average effect of a given technique. Comparisons can then be made about the relative effectiveness of various techniques for increasing student achievement. Meta analysis involves identifying, collecting, reviewing, coding, and interpreting scientific research studies. Study outcomes are translated to a common metric to allow results to be compared. Following the explanation of concepts important to meta analysis, the Digest provides an example and lists some resources for further information and tips for locating examples of meta analysis. (Contains 10 references.) (SLD)