Types of systematic reviews
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
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.
- Example of a qualitative systematic review:
Phillips P, Lumley E, Duncan R et al. A systematic review of qualitative research into people’s experiences of living with venous leg ulcers. J Adv Nurs 2018;74:550-63.
https://onlinelibrary.wiley.com/doi/abs/10.1111/jan.13465 - Example of a qualitative systematic review, termed a “meta-synthesis”:
Behzadifar M, Bragazzi NL, Arab-Zozani M et al. The challenges of implementation of clinical governance in Iran: a meta-synthesis of qualitative studies. Health Res Policy Syst 2019;17:3.
https://health-policy-systems.biomedcentral.com/articles/10.1186/s12961-018-0399-5
Quantitative systematic reviews
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).
- Example of a meta-analysis of observational studies, reflected in title:
Khan MF, Brilakis ES, Wendel CS, Thai H. Comparison of procedural complications and in-hospital clinical outcomes between patients with successful and failed percutaneous intervention of coronary chronic total occlusions: a meta-analysis of observational studies. Catheter Cardiovasc Interv 2015;85:781-94.
https://onlinelibrary.wiley.com/doi/full/10.1002/ccd.25712 - Example of a meta-analysis of clinical trials, reflected in title:
Navickis RJ, Greenhalgh D, Wilkes MM. Albumin in burn shock resuscitation: a meta-analysis of controlled clinical studies. J Burn Care Res 2016;37:e268-78.
https://academic.oup.com/jbcr/article/37/3/e268/4582152 - Example of a meta-analysis of both observational studies and clinical trials, reflected in title:
Chua ME, Gnech M, Ming JM. Preoperative hormonal stimulation effect on hypospadias repair complications: meta-analysis of observational versus randomized controlled studies. J Pediatr Urol 2017;13:470-80.
https://www.jpurol.com/article/S1477-5131(17)30289-9/fulltext - Example of a meta-analysis of both observational studies and clinical trials, but title only says “systematic review”:
Heiney SP, Parker PD, Felder TM, Adams SA, Omofuma OO, Hulett JM. A systematic review of interventions to improve adherence to endocrine therapy. Breast Cancer Res Treat 2019;173:499-510.
https://link.springer.com/article/10.1007%2Fs10549-018-5012-7
Mixed-Methods systematic reviews
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.
- Example of a mixed-methods systematic review:
Guillaumie L, Boiral O, Champagne J. A mixed-methods systematic review of the effects of mindfulness on nurses. J Adv Nurs 2017;73:1017-34.
https://onlinelibrary.wiley.com/doi/abs/10.1111/jan.13176
- Example of a mixed-methods systematic review, simply termed a “systematic review”:
Maund E, Stuart B, Moore M et al. Managing antidepressant discontinuation: a systematic review. Ann Fam Med 2019;17:52-60.
http://www.annfammed.org/content/17/1/52.long
- Example of a mixed-methods systematic review, termed a “systematic review and meta-analysis”:
Tang R, Wang J, Yang L et al. Subclinical hypothyroidism and depression: a systematic review and meta-analysis. Front Endocrinol 2019;10:340.
https://www.frontiersin.org/articles/10.3389/fendo.2019.00340/full#F1
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.
Other types of systematic reviews
Below are four other types of systematic reviews. Click each type to learn more and to see real-world examples.
Diagnostic test accuracy review
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).
- Example of a systematic review that is a “diagnostic test accuracy review”:
de Joode JW, van Dijk SEM, Walburg FS et al. Diagnostic accuracy of depression questionnaires in adult patients with diabetes: a systematic review and meta-analysis. PLoS One 2019;14:e0218512.
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0218512
Network meta-analysis
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).
- Example of a systematic review that is a “network meta-analysis”:
Sbidian E, Chaimani A, Garcia-Doval I et al. Systemic pharmacological treatments for chronic plaque psoriasis: a network meta-analysis. Cochrane Database Syst Rev 2017;12:CD011535.
https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD011535.pub2/full
Umbrella review (‘systematic review of systematic reviews’)
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.
- Example of a systematic review that is an “umbrella review” of systematic reviews (including meta-analyses):
Veronese N, Demurtas J, Celotto S et al. Is chocolate consumption associated with health outcomes? An umbrella review of systematic reviews and meta-analyses. Clin Nutr 2019;38:1101-8.
https://www.sciencedirect.com/science/article/pii/S0261561418302048
Scoping reviews and integrative reviews
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.
- Example of a “scoping review”:
van Kampen SC, Wanner A, Edwards M et al. International research and guidelines on post-tuberculosis chronic lung disorders: a systematic scoping review. BMJ Glob Health 2018;3:e000745.
https://gh.bmj.com/content/3/4/e000745
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.
- Example of an “integrative review”:
Taylor SL, Leffers JM. Integrative review of service-learning assessment in nursing education. Nurs Educ Perspect 2016;37:194-200.
https://insights.ovid.com/pubmed?pmid=27740577