Synthesis of research findings has long been a part of reviewing and summarizing a field of
study. Public health decisions are made on the available evidence. We summarize the
approaches to research synthesis that draw on the best available evidence and the use of
quantitative summaries through meta-analysis. We focus on observational studies.
Heterogeneity offers the potential to observe a relation across study populations and
circumstances. We emphasize the benefits of heterogeneity in overviews and the need to …