Systematic review, meta-analysis, and research synthesis

When researchers review available literature on various topics they often have to face the situation of finding a large number of studies reporting contradictory results. In these cases, meta-analysis is the best procedure to produce trustworthy research syntheses and to test factors that can explain heterogeneity of results reported in primary studies.

What is a systematic review?

A systematic review (or research synthesis) is a review of an area of study based on a clearly formulated research question that uses systematic and explicit methods to identify, select, and evaluate relevant research. A systematic review (research synthesis) can use statistical techniques to provide a quantitative summary of study results.

What is the true meaning of meta-analysis?

The meta-analysis refers to a systematic review/research synthesis that provides a statistical synthesis of an area of study. Researchers can use the term meta-analysis in two ways:

a) to refer specifically to the statistical section included in a systematic review/research synthesis (e.g., Gender differences in anxiety: A systematic review and meta-analysis)

b) as a synonymous of a systematic review/research synthesis including a statistical section (e.g., Gender differences in anxiety: A meta-analysis)

Throughout this website we use the term meta-analysis in this second way.

Meta-analysis, introduced in the 70s by Gene Glass to test the effectiveness of psychotherapy, is now widely applied in various fields (e.g., psychological, educational, medical, etc.). Meta-analysis is used to address several research questions, such as:

• Is a particular treatment effective? (e.g., is an experimental drug effective?)
• Are there differences between two groups? (e.g., do adopted children and biological children exhibit different levels of self-esteem?)
• Are two variables related? (e.g., is job satisfaction associated with family satisfaction?)

To answer these questions, meta-analysis provides a quantitative synthesis of study results available in a specific area of research.

Once the research question is clear, conducting a meta-analysis involves a series of well-defined steps, from defining the research area to publishing the results — see Meta-analysis steps for the full process.