Why do we need reviews?
With advances in medical practice and fields of research, reviews occupy a key position for summarizing existing knowledge. Literature review helps to provide context for research, show where research fits into the existing body of knowledge, and enable the researcher to learn from previous studies on the subject. As well as, outline gaps in previous studies, illustrate whether the review is adding to the understanding and knowledge of the field, help make decisions, and produce results that change the practice.
Types of reviews:
There are many different types of literature reviews, each with its own approach, analysis, and purpose. The following table is reproduced from the study done by Grant and Booth analyzing 14 review types and associated methodologies using a simple analytical framework: Search, Appraisal, Synthesis and Analysis (SALSA).
|
Label |
Description |
Methods used (SALSA) |
|||
|---|---|---|---|---|---|
|
Search |
Appraisal |
Synthesis |
Analysis |
||
| Literature review | Generic term: published materials that provide an examination of recent or current literature. It can cover a wide range of subjects at various levels of completeness and comprehensiveness. May include research findings | May or may not include comprehensive searching | May or may not include quality assessment | Typically narrative | The analysis may be chronological, conceptual, thematic, etc. |
| Systematic review | Seeks to systematically search for, appraise and synthesis research evidence, often adhering to guidelines on the conduct of a review | Aims for exhaustive, comprehensive searching | 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 |
| Meta-analysis | A technique that statistically combines the results of quantitative studies to provide a more precise effect of the results | Aims for exhaustive, comprehensive searching. May use funnel plot to assess the completeness | Quality assessment may determine inclusion/exclusion and/or sensitivity analyses | Graphical and tabular with a narrative commentary | Numerical analysis of measures of effect assuming the absence of heterogeneity |
| Scoping review | Preliminary assessment of potential size and scope of available research literature. Aims to identify nature and extent of research evidence (usually including ongoing research) | Completeness of searching determined by time/scope constraints. May include research in progress | No formal quality assessment | Typically tabular with some narrative commentary | Characterizes quantity and quality of literature, perhaps by study design and other key features. Attempts to specify a viable review |
| Rapid review | Assessment of what is already known about a policy or practice issue, by using systematic review methods to search and critically appraise existing research | Completeness of searching determined by time constraints | Time-limited formal quality assessment | Typically narrative and tabular | Quantities of literature and overall quality/direction of effect of literature |
|
Critical review |
Aims to demonstrate the writer has extensively researched literature and critically evaluated its quality. Goes beyond mere description to include a degree of analysis and conceptual innovation. Typically results in hypothesis or model |
Seeks to identify the most significant items in the field |
No formal quality assessment. Attempts to evaluate according to a contribution |
Typically narrative, perhaps conceptual or chronological |
Significant component: seeks to identify conceptual contribution to embody existing or derive a new theory |
|
Mapping review/ systematic map |
Map out and categorize existing literature from which to commission further reviews and/or primary research by identifying gaps in research literature |
Completeness of searching determined by time/scope constraints |
No formal quality assessment |
May be graphical and tabular |
Characterizes quantity and quality of literature, perhaps by study design and other key features. May identify a need for primary or secondary research |
|
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 conceived quantitative and qualitative strategies |
Requires either a generic appraisal instrument or separate appraisal processes with corresponding checklists |
Typically both components will be presented as narrative and in tables. May also employ graphical means of integrating quantitative and qualitative studies |
The analysis may characterize both literatures and 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 the [medical] literature that attempts to survey the literature and describe its characteristics |
May or may not include comprehensive searching (depends whether systematic overview or not) |
May or may not include quality assessment (depends whether systematic overview or not) |
Synthesis depends on whether systematic or not. Typically narrative but may include tabular features |
The analysis may be chronological, conceptual, thematic, etc. |
|
Qualitative systematic review/qualitative evidence synthesis |
Method for integrating or comparing the findings from qualitative studies. It 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 |
A qualitative, narrative synthesis |
The thematic analysis may include conceptual models |
|
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 searching of current literature |
No formal quality assessment |
Typically narrative may have tabular accompaniment |
The current state of knowledge and priorities for future investigation and research |
|
Systematic search and review |
Combines the strengths of critical review with a comprehensive search process. Typically addresses broad questions to produce ‘best evidence synthesis’ |
Aims for exhaustive, comprehensive searching |
May or may not include quality assessment |
Minimal narrative, a tabular summary of studies |
What is known; recommendations for practice. Limitations |
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