What is a meta-analysis? Meta-analysis refers to a set of statistical methods to synthesize the quantitative results of studies. A meta-analysis is usually conducted when one of the goals of the systematic review is to examine the magnitude (how much) and the sign (positive or negative) of the relationship between the variables of interest that are conceptualized in the research synthesis process. These quantitative procedures include the use of effect sizes that represent the quantitative results of included studies. These effect sizes can both measure the magnitude and sign of relationships between variables in a systematic review and analysis, and as such, producing effect sizes is a foundational step conducting a meta-analysis.
One common misconception in research synthesis is confusion around the difference between a systematic review and a meta-analysis. A systematic review refers to the process of identifying, retrieving, and appraising primary studies for relevant characteristics as determined by the research question. A meta-analysis refers to the set of statistical methods for analyzing effect sizes in a systematic review. Systematic reviews and meta-analyses are often performed together. However, not every systematic review will use meta-analytic techniques depending on the the research question. Below is a (non-exhaustive) list of the types of systematic review questions that would use meta-analysis:
The systematic review focuses on estimating the effectiveness of an intervention and the heterogeneity in effects of the intervention.
The systematic review focuses on estimating the differences between two groups and the heterogeneity among studies in this difference.
The systematic review focuses on estimating the correlation or association between constructs, examining the average correlation and its heterogeneity among studies or estimating a path model among a set of constructs