While systematic reviews are a very popular type of evidence synthesis, they are not the only type of review you can conduct, and may not be the best fit for what you want to do. This page presents the components of many different review types to help you think about the appropriateness of each for your research project.
This decision tree from Cornell University and the Right Review tool can help you determine which review is best for your project.
Adapted with minimal changes from: Grant, M. J., & Booth, A. (2009). A typology of reviews: An analysis of 14 review types and associated methodologies. Health Information and Libraries Journal, 26(2), 91–108. https://doi.org/10.1111/j.1471-1842.2009.00848.x PMID: 19490148
| Review Type | Description | Search | Appraisal | Synthesis | Analysis |
|
Critical review |
Aims to demonstrate writer has extensively researched & critically evaluated literature. Includes analysis & conceptual innovation. Typically results in hypothesis or model | Seeks to identify most significant items in the field | No formal quality assessment. Attempts to evaluate according to contribution | Typically narrative. Perhaps conceptual or chronological | Significant analysis: seeks to identify conceptual contribution to embody existing or derive new theory |
|
Literature review |
Generic term: published materials that provide examination of recent or current literature. Can cover wide range of subjects & vary in comprehensiveness. May include research findings |
May include comprehensive search. Not required | May include quality assessment. Not required | Typically narrative | Analysis may be chronological, conceptual, thematic, etc. |
| Mapping review | Map out & categorize existing literature to identify gaps in research literature. Provides direction for further reviews and/or primary research | Completeness of search determined by time/scope constraints | No formal quality assessment | May be graphical & tabular | Characterizes quantity & quality of literature by study design or other key features. May identify need for primary or secondary research |
| Meta-analysis | Statistically combine results of quantitative studies to provide overall effect size of results | Aims for comprehensive search | Quality assessment may determine inclusion/exclusion &/or sensitivity analyses | Graphical & tabular with narrative commentary | Numerical analysis of effect assuming absence of heterogeneity |
| Mixed methods review | Refers to any combination of methods where one significant component is a literature review (usually systematic). Within a review context it refers to a combination of review approaches for example combining quantitative with qualitative research or outcome with process studies | Requires either very sensitive search to retrieve all studies or separately developed quantitative & qualitative strategies | Requires either a generic appraisal instrument or separate appraisal processes with corresponding checklists | Typically both components are presented as narrative & in tables. May also employ graphical means of integrating quantitative and qualitative studies | Analysis may characterize both literatures & look for correlations between characteristics or use gap analysis to identify aspects absent in one literature but missing in the other |
| Overview | Generic term: summary of [medical] literature that attempts to survey the literature & describe its characteristics | May include comprehensive search | May include quality assessment (depends whether systematic overview or not) | Synthesis depends on whether systematic or not. Typically narrative but may include tabular features | Analysis may be chronological, conceptual, thematic, etc. |
| Qualitative systematic review | Method for integrating or comparing findings from qualitative studies. Looks for ‘themes’ or ‘constructs’ that lie in or across individual qualitative studies | May employ selective or purposive sampling | Quality assessment typically used to mediate messages, not for inclusion/exclusion | Qualitative, narrative synthesis | Thematic analysis, may include conceptual models |
| Rapid review | Assessment of what is already known about a policy or practice issue, by using systematic review methods to search & critically appraise existing research | Completeness of search determined by time constraints | Time-limited formal quality assessment | Typically narrative & tabular | Quantities of literature & overall quality/direction of effect of literature |
| Scoping review | Preliminary assessment of potential size & scope of available research literature. Aims to identify nature & extent of research evidence (usually including ongoing research) | Completeness of search determined by time/scope constraints. May include research in progress |
No formal quality assessment | Typically tabular with some narrative commentary | Characterizes quantity & quality of literature, perhaps by study design & other key features. Attempts to specify a viable review |
| State-of-the-art review | Tend to address more current matters in contrast to other combined retrospective and current approaches. May offer new perspectives on issue or point out area for further research | Aims for comprehensive search of current literature | No formal quality assessment | Typically narrative, may have tabular accompaniment | Current state of knowledge & priorities for future investigation and research |
| Systematic review | Seeks to systematically search for, appraise & synthesize research evidence, often adhering to guidelines on the conduct of a review | Aims for exhaustive, comprehensive search | Quality assessment may determine inclusion/exclusion | Typically narrative with tabular accompaniment | What is known; recommendations for practice. What remains unknown; uncertainty around findings, recommendations for future research |
| Systematic search & review | Combines strengths of critical review with comprehensive search. Typically addresses broad questions to produce ‘best evidence synthesis’ | Aims for exhaustive, comprehensive search | May include quality assessment | Minimal narrative, tabular summary of studies | What is known; recommendations for practice. Limitations |
| Systematized review | Attempt to include elements of systematic review process while stopping short of systematic review. Typically conducted as postgraduate student assignment | May include comprehensive search | May include quality assessment | Typically narrative with tabular accompaniment | What is known; uncertainty around findings; limitations of methodology |
| Umbrella review | Review of reviews. Compiles evidence from multiple reviews into one accessible and usable document. Focuses on broad condition or problem for which there are competing interventions and highlights reviews that address these interventions & their results | Identification of component reviews, but no search for primary studies, i.e. search for reviews only | Quality assessment of studies within component reviews &/or of reviews themselves | Graphical & tabular with narrative commentary | What is known; recommendations for practice. What remains unknown; recommendations for future research |
While not nearly as comprehensive, you may find the below flowchart from Cornell University helpful to consider as well. It will walk you through a series of questions to help you narrow in on an appropriate type of review.