A systematic review is a research summary that addresses a focused question in a structured and reproducible manner. With this, systematic reviews are conducted according to stringent guidelines to minimize bias and maintain scientific integrity. This stands in contrast to the traditional expert review in which field adepts collate a summary on a particular topic of interest (Table 1). Such expert reviews can be useful for obtaining a broad overview on certain fields. However, concerns have been raised that such traditional reviews are biased, e.g., by arbitrary inclusion of articles and lack of critical appraisal of discussed studies.
| Narrative review | Systematic review | |
|---|---|---|
| Research question | Often broad or unclear | More focused and specific |
| Evidence source(s) | Not usually specified | More comprehensive, based on explicit search strategy |
| Study selection | Not usually specified | Explicit eligibility criteria and selection by two independent reviewers |
| Quality assessment of eligible studies | Not usually present or only implicit | Critical appraisal based on explicit quality criteria |
| Synthesis | Commonly a qualitative summary | Often also meta-analysis, i.e., quantitative summary |
Adjusted from De Vries et al. (2014)
What is a meta-analysis The more qualitative aspect of systematic review can be complemented by a quantitative approach, i.e., a meta-analysis. A meta-analysis is a statistical method pooling different study measures to create a single estimate of outcomes. Meta-analyses can also be helpful to evaluate heterogeneity among eligible references and to probe the publication bias within a field. Together, systematic reviews and meta-analyses are considered to represent the highest level in the hierarchy of evidence.
What is a meta-analysis?
The more qualitative aspect of systematic review can be complemented by a quantitative approach, i.e., a meta-analysis. A meta-analysis is a statistical method pooling different study measures to create a single estimate of outcomes. Meta-analyses can also be helpful to evaluate heterogeneity among eligible references and to probe the publication bias within a field. Together, systematic reviews and meta-analyses are considered to represent the highest level in the hierarchy of evidence.
References and further reading
de Vries RB, Wever KE, Avey MT, Stephens ML, Sena ES, Leenaars M. The usefulness of systematic reviews of animal experiments for the design of preclinical and clinical studies. ILAR J. 2014;55(3):427-37.. PMID: 25541545; PMCID: PMC4276599. doi: https://doi.org/10.1093/ilar/ilu043
Egger, M., Higgins, J. P. & Smith, G. D. Systematic reviews in health research: Meta-analysis in context. (John Wiley & Sons, 2022).