The reviews selected for inclusion in the Best Evidence Encyclopedia are meta-analyses or other quantitative syntheses that apply consistent, scientific standards to bodies of evidence that both meet high standards of methodological quality and evaluate realistic implementations of programs currently available to educators. Specifically, to be included, reviews must:
- Consider all studies in their area, and carry out an exhaustive search for all studies that meet well-justified standards of methodological quality and relevance to the issue being reviewed.
- Present quantitative summaries of evidence on the effectiveness of programs or practices used with children in grades K-12, focusing on achievement outcomes.
- Focus on studies comparing programs to control groups, with random assignment to conditions or matching on pretests or other variables that indicate that experimental and control groups were equivalent before the treatments began.
- Summarize program outcomes in terms of effect sizes (experimental-control differences divided by the standard deviation) as well as statistical significance.
- Focus on studies that took place over periods of at least 12 weeks, to avoid brief, artificial laboratory studies.
- Focus on studies that used measures that assessed the content studied by control as well as experimental students, to avoid studies that used measures inherent to the experimental treatment