The key difference between systematic review and evidence synthesis lies in their scope: evidence synthesis is a broad umbrella term encompassing various methods, while a systematic review is a specific, rigorous type of evidence synthesis.
Evidence synthesis refers to any method of identifying, selecting, and combining results from multiple studies to create a comprehensive understanding of a particular topic. Systematic reviews and literature reviews are two methods of identifying and providing summaries of existing literature.
Understanding Evidence Synthesis
Evidence synthesis is the overarching process of bringing together findings from different studies to answer a particular research question, inform policy, or guide practice. It is a critical step in evidence-based decision-making across fields like healthcare, education, and social sciences.
Characteristics of Evidence Synthesis:
- Broad Scope: Can include a wide array of methodologies, from highly structured to more exploratory.
- Purpose-Driven: Aims to synthesize existing knowledge to identify gaps, inform guidelines, or understand complex phenomena.
- Variety of Methods: Includes systematic reviews, meta-analyses, scoping reviews, rapid reviews, narrative syntheses, and qualitative syntheses.
- Flexibility: The rigor and comprehensiveness can vary depending on the chosen method and the research question.
For instance, a scoping review might be used to map the existing literature on a broad topic, identifying key concepts, study types, and research gaps, without necessarily critically appraising the quality of individual studies.
Systematic Review: A Methodological Gold Standard
A systematic review is a highly structured and meticulous form of evidence synthesis. It employs a predefined, explicit methodology to identify, select, critically appraise, and synthesize all relevant research on a particular topic. The goal is to minimize bias and provide a reliable summary of the evidence.
Key Features of a Systematic Review:
- Clear, Focused Question: Begins with a well-defined and answerable research question (e.g., using PICO format).
- Comprehensive Search Strategy: Uses exhaustive and reproducible searches across multiple databases and grey literature to identify all relevant studies.
- Explicit Inclusion/Exclusion Criteria: Studies are selected based on transparent and predefined criteria.
- Rigorous Critical Appraisal: Each included study is systematically assessed for methodological quality and risk of bias.
- Data Extraction: Relevant data from selected studies are extracted systematically.
- Synthesis of Findings: Results are combined qualitatively (narrative synthesis) or quantitatively (meta-analysis) to present a summary of the evidence.
- Minimizes Bias: The systematic approach aims to reduce researcher bias at every stage.
An example of a systematic review might be to evaluate the effectiveness of a specific medication for a particular condition by pooling data from multiple randomized controlled trials.
Comparing Systematic Review and Evidence Synthesis
The relationship can be thought of as a set: all systematic reviews are a form of evidence synthesis, but not all evidence syntheses are systematic reviews.
Here’s a table highlighting their key differences:
| Feature | Evidence Synthesis | Systematic Review |
|---|---|---|
| Scope | Broad umbrella term, encompasses many methods. | Specific, highly structured method of evidence synthesis. |
| Methodology | Varies widely depending on the chosen synthesis approach. | Strict, predefined, explicit, and reproducible protocol. |
| Rigor/Bias | Rigor varies; some methods may be less focused on bias minimization. | High rigor, explicitly designed to minimize bias. |
| Research Question | Can address broad or exploratory questions. | Addresses a clearly defined, focused question. |
| Search Strategy | Can be comprehensive or more targeted; varies by method. | Exhaustive and transparent search across multiple sources. |
| Critical Appraisal | May or may not include formal quality assessment. | Essential component; rigorous assessment of study quality. |
| Time/Resources | Can range from rapid to extensive, depending on the method. | Typically resource-intensive and time-consuming. |
| Examples | Scoping reviews, rapid reviews, narrative reviews, meta-analyses, systematic reviews. | Only systematic reviews (often including meta-analysis). |
Practical Implications
Understanding this distinction is crucial for researchers, practitioners, and policymakers:
- Choosing the Right Method: When you need a definitive answer to a focused question with minimal bias, a systematic review is the appropriate choice. If you need to map existing literature, explore concepts, or quickly summarize evidence, other evidence synthesis methods might be more suitable.
- Interpreting Findings: Knowing the method used for synthesis helps in critically evaluating the strength and generalizability of the conclusions. A conclusion from a systematic review generally carries more weight due to its rigorous methodology compared to a less structured literature review.
- Resource Allocation: Systematic reviews require significant time, expertise, and resources, which should be considered when planning a research project.
By employing appropriate evidence synthesis methods, including the highly rigorous systematic review, researchers can provide robust, reliable information to guide decision-making and advance knowledge.
