There are two main types of systematic review: Qualitative (sometimes termed “meta-synthesis”) and quantitative (typically termed “meta-analysis”).
A “mixed-methods systematic review” or “systematic review and meta-analysis” contains both qualitative and quantitative components.
Click each type below to learn more:
Qualitative systematic reviews evaluate, summarize, and interpret data that are not numerical, such as descriptive results, observations, texts, and transcripts. Observational study types that can be included in such reviews include interviews, surveys, questionnaires, focus-group studies, diary studies, and case studies/reports.
In contrast, quantitative systematic reviews or meta-analyses involve pooling the numerical data from two or more studies and using appropriate statistical tests to analyze the combined data. Study types that can be included in such reviews include quantitative case studies/reports/series, observational epidemiologic studies (eg, cross-sectional studies, case-control studies, retrospective or prospective cohort studies), and clinical trials (non-randomized controlled trials, quasi-randomized controlled trials, and randomized controlled trials).
A “mixed-methods systematic review” or “systematic review and meta-analysis” contains an initial general qualitative summary followed by a sub-analysis of relevant numerical data in a meta-analysis.
The wide variation in naming of systematic reviews can be confusing. It is very important for authors to document the exact review methods used, so that readers can know what type of systematic review they are reading.
Below are four other types of systematic reviews. Click each type to learn more and to see real-world examples.
One related type of review is the diagnostic test accuracy review, which includes a meta-analysis of pooled data from tests and interventions (eg, sensitivity and specificity).
A network meta-analysis is a meta-analysis of randomized controlled trials that together have compared three or more interventions/treatments. In a standard meta-analysis, the same pair of treatments is directly compared (eg, A versus B). However, a network meta-analysis can also evaluate indirect evidence, where treatments are indirectly compared if the individual studies share a common comparator (eg, trials of A versus B and B versus C could allow an indirect treatment comparison of A versus C).
A systematic review of systematic reviews is termed an umbrella review. These reviews can be qualitative or quantitative or both, and are performed to help decision-makers when there are multiple systematic reviews on the same research question.
Scoping reviews and integrative reviews are not strictly systematic reviews, because they do not follow all the rules in performing the review. The research questions are typically broad and exploratory, because the aim is to obtain a comprehensive overview of a new topic or area and to suggest future research directions. The included studies may be of a lower quality and have a wider range of design types.
Scoping reviews measure the amount, types, extent, and key content of research evidence on a specific topic, and study how the literature on that topic has developed over time.
Integrative reviews find commonalities from multiple perspectives of a general problem or issue (often in the social sciences), including theoretical aspects, and typically identify overall themes.