Key Characteristics:
* Reproducibility: The methods are explicitly documented, allowing others to replicate the review process and potentially arrive at similar conclusions. This is crucial for transparency and credibility.
* Comprehensive Search Strategy: A meticulously planned search strategy is used to identify all relevant studies, regardless of publication status (published and unpublished, grey literature). This minimizes bias due to publication bias (where only positive results are published).
* Explicit Inclusion/Exclusion Criteria: Pre-defined criteria are used to select studies for inclusion, ensuring consistency and reducing subjective bias in study selection. These criteria are based on the research question and may relate to study design, population, interventions, outcomes, and publication year.
* Critical Appraisal of Included Studies: Each included study undergoes rigorous quality assessment using predetermined tools and checklists to assess the methodological rigor and risk of bias. This allows for an understanding of the strength of evidence provided by each individual study.
* Data Extraction and Synthesis: Data relevant to the research question are extracted from the included studies in a standardized way. This extracted data is then synthesized using appropriate statistical or qualitative methods, depending on the type of data and research question.
* Assessment of Heterogeneity: Systematic reviews assess the extent to which the results of the included studies are consistent (homogeneity) or vary (heterogeneity). Heterogeneity necessitates exploration of potential reasons for the variability and may influence the choice of synthesis method (e.g., meta-analysis may be inappropriate with high heterogeneity).
* Transparency and Reporting: Systematic reviews adhere to established reporting guidelines (e.g., PRISMA statement), ensuring that all aspects of the review process are clearly reported, enhancing transparency and facilitating critical appraisal by others.
Methodologies:
1. Formulating the Research Question: A clear, focused, and answerable research question (often using PICO – Population, Intervention, Comparison, Outcome) guides the entire review process.
2. Developing the Search Strategy: This involves identifying relevant databases, keywords, and search terms to retrieve studies. The search strategy is typically iterative, refined as the review progresses.
3. Study Selection: Titles and abstracts are screened initially, followed by full-text screening of potentially relevant studies based on the pre-defined inclusion and exclusion criteria. This process is typically conducted independently by two or more reviewers to minimize bias. Disagreements are resolved through discussion or consultation with a third reviewer.
4. Data Extraction and Management: A data extraction form is used to collect relevant data from each included study consistently. This data is usually entered into a database for analysis.
5. Risk of Bias Assessment: Using validated tools, the risk of bias in each included study is assessed. This helps evaluate the credibility of the findings of individual studies and the overall review.
6. Data Synthesis: Depending on the nature of the data (e.g., continuous, dichotomous) and the degree of heterogeneity, different methods of synthesis are used. Meta-analysis (statistical pooling of data) is often used for quantitative data if there is sufficient homogeneity, while narrative synthesis is used for qualitative data or when significant heterogeneity is present.
7. Interpretation of Findings: The results of the synthesis are interpreted in light of the limitations of the review and the quality of the included studies. The findings are presented in a clear and concise manner.
By adhering to these characteristics and methodologies, systematic reviews aim to provide a reliable and comprehensive summary of the existing evidence on a particular topic, informing clinical practice, policy decisions, and future research.