Generalizability and Research Synthesis
Many authors have written about the generalizability-or external validity-of single studies. Generalizability, along with internal validity, is a key factor in what we can learn from a study. Obviously, generalizability relates most closely to external validity-or the question of whether the results of a study apply beyond the exact situations (subjects, conditions, etc.) that are examined in the study (or in our case, the studies) at hand. In this chapter, we are concerned with the issue of generalizability in meta-analysis or quantitative research synthesis, which has not been discussed much by meta-analysts or methodologists who study meta-analysis.