Coding the Studies Each of the studies included in the analyses was coded with respect to the moderator variables described above as well as general study characteristics. A thorough coding manual including instructions for coding articles and abstracting appropriate effect sizes was developed in order to aid in the coding process. All studies were coded by at least two researchers. The researchers agreed on 89.5% of the initial codes, and disagreements were resolved via discussion. Additionally, reliability estimates (alpha) of the effectiveness measure from each study were recorded. Finally, all relevant information was coded to aid in the calculation of the standardized mean difference effect size.