ABSTRACT
A meta-analysis is a combination of existing primary studies on a particular problem and a clarification of the differences among their results. Meta-analyses have a longer tradition in English educational science. When Visible Learning was published in 2008, already 15 years of work were invested – collecting, viewing, and evaluating about 800 meta-analyses during that time. These meta-analyses themselves included over 50,000 primary studies, in which an estimated 200 million learners participated. In order to put the insights included in Visible Learning in the proper context, it is necessary to point out the advantages and disadvantages of meta-analysis. A meta-analysis might examine the impact of class size on learners’ mathematical achievements. Meta-analysis is used primarily in cases where a problem has already been researched extensively and a number of quantitative-empirical results are available.
