Systematic Review:
* Explicit, pre-defined methodology: A systematic review follows a pre-defined protocol, outlining the specific research question, inclusion/exclusion criteria for studies, search strategy, data extraction methods, and risk of bias assessment. This protocol is often registered in a database to ensure transparency and minimize bias.
* Comprehensive search strategy: It involves a meticulous search of multiple databases (e.g., PubMed, Web of Science, Embase) and other sources (e.g., grey literature, conference proceedings) to identify *all* relevant studies, regardless of publication status or language (within feasible limits).
* Explicit quality assessment: Each included study undergoes a critical appraisal to assess its methodological quality and risk of bias. This helps to determine the trustworthiness of the evidence from each individual study.
* Explicit data extraction: Data relevant to the research question are systematically extracted from each included study using a standardized form.
* Synthesis of findings: The extracted data are then synthesized using appropriate statistical methods (e.g., meta-analysis for quantitative data, thematic analysis for qualitative data) to provide a summary of the evidence and address the research question.
* Transparency and reproducibility: The entire process, from the protocol to the results, is meticulously documented, allowing for replication and evaluation by others.
Other Types of Literature Reviews (in comparison):
* Narrative review: This is a more traditional approach that is less rigorous and systematic. It often lacks a clearly defined research question or methodology, and the selection of studies may be subjective and based on the author's knowledge and judgment. The synthesis is often descriptive rather than analytical.
* Scoping review: Aims to map the breadth and depth of literature on a topic, identify gaps in research, and explore concepts rather than definitively answering a specific research question. It is less rigorous in terms of study selection and quality assessment than a systematic review.
* Integrative review: Combines both quantitative and qualitative research to provide a comprehensive understanding of a topic. The methodology can vary but typically involves a systematic search and critical appraisal of studies, although often less rigorous than a systematic review.
Key Differences Summarized:
| Feature | Systematic Review | Narrative Review | Scoping Review |
|-----------------|-------------------------------------------------|-----------------------------------------------|-----------------------------------------------|
| Research Question | Explicit, clearly defined | Often implicit or broadly defined | Broad, exploring a concept or area |
| Search Strategy | Exhaustive, pre-defined, multiple databases | Selective, based on author's knowledge | Broad, aiming for comprehensiveness but less exhaustive |
| Study Selection | Explicit inclusion/exclusion criteria, rigorous | Subjective, based on author's judgment | Less stringent criteria, broad inclusion |
| Quality Assessment| Rigorous, standardized assessment of risk of bias | Often lacking or minimal | Often less rigorous than systematic reviews |
| Synthesis | Statistical (meta-analysis) or qualitative | Narrative, descriptive | Mapping, identifying gaps and trends |
| Transparency | High, detailed protocol and methods documented | Low, methods often poorly described | Moderate, methods described but less detail than systematic reviews |
In essence, a systematic review strives for the highest level of rigor and transparency to provide the most reliable and unbiased summary of existing evidence on a specific topic. This makes it the gold standard for informing evidence-based practice and policy decisions.