A history of meta-regression: Technical, conceptual, and practical developments between 1974 and 2018.

At the beginning of the development of meta-analysis, understanding the role of moderators was given the highest priority, with meta-regression provided as a method for achieving this goal. Yet in current practice, meta-regression is not as commonly used as anticipated. This paper seeks to understand this mismatch by reviewing the history of meta-regression methods over the past 40 years. We divide this time span into four periods and examine three types of methodological developments within each period: technical, conceptual, and practical. Our focus is broad and includes development of methods in the fields of education, psychology, and medicine. We conclude the paper with a discussion of five consensus points, as well as open questions and areas of research for the future.