Embarking on a systematic literature review (SLR) is a rigorous and methodical approach to identifying, evaluating, and synthesizing all relevant studies on a specific research question. A standalone SLR, unlike those embedded within a larger study, serves as a self-contained research project, offering valuable insights and informing future research directions. This guide provides a detailed overview of the steps involved in conducting a standalone SLR, ensuring a comprehensive and transparent process.
1. Defining the Research Question and Scope
The cornerstone of any SLR is a well-defined research question. This question should be focused, answerable, and relevant to the existing body of knowledge. The PICOS framework (Population, Intervention, Comparison, Outcome, Study design) can be a useful tool for structuring your research question.
Consider these examples:
- Poor: What are the effects of social media? (Too broad)
- Better: What is the impact of social media use on the academic performance of undergraduate students? (More focused)
- Best: In undergraduate students (Population), what is the effect of daily social media use for more than 2 hours (Intervention) compared to less than 1 hour (Comparison) on their GPA (Outcome), as measured in cohort studies (Study Design)?
Clearly defining the scope of your review is equally crucial. This involves specifying the inclusion and exclusion criteria for studies, including the types of populations, interventions, outcomes, and study designs that will be considered.
2. Developing a Search Strategy
A comprehensive search strategy is essential for identifying all relevant studies. This involves:
- Identifying relevant databases: Examples include Scopus, Web of Science, PubMed, and Google Scholar.
- Developing search terms: Utilize keywords, synonyms, and related terms to capture all relevant literature. Boolean operators (AND, OR, NOT) can be used to refine your search.
- Pilot testing: Test your search strategy in a few databases to ensure it retrieves relevant articles.
- Documenting your search process: Maintain a detailed record of your search terms, databases searched, and the dates of your searches. This ensures transparency and replicability.
3. Screening and Selecting Studies
The screening process involves reviewing the titles and abstracts of retrieved articles to determine their eligibility based on your inclusion and exclusion criteria.
- Title and abstract screening: This initial screening helps to eliminate irrelevant articles quickly.
- Full-text screening: Obtain the full text of potentially relevant articles and assess them against your inclusion and exclusion criteria.
- Using screening tools: Software such as Covidence or Rayyan can streamline the screening process, especially for large numbers of articles.
- Inter-rater reliability: If possible, have two or more reviewers independently screen the articles to ensure consistency and reduce bias. Calculate inter-rater reliability using Cohen’s Kappa coefficient.
4. Data Extraction
Data extraction involves systematically collecting relevant information from the included studies. This may include:
- Study characteristics: Author, year, study design, sample size.
- Population characteristics: Age, gender, demographics.
- Intervention characteristics: Type of intervention, dosage, duration.
- Outcome measures: Primary and secondary outcomes, measurement methods.
- Results: Statistical data, effect sizes, confidence intervals.
Use a standardized data extraction form to ensure consistency. Pilot test the form on a few articles to identify any necessary revisions.
5. Assessing the Quality of Included Studies
Assessing the methodological quality (or risk of bias) of included studies is crucial for interpreting the results of your SLR. Several tools are available for assessing different study designs. Examples include:
- Cochrane Risk of Bias Tool (RoB 2): For randomized controlled trials.
- Newcastle-Ottawa Scale (NOS): For observational studies.
- Critical Appraisal Skills Programme (CASP) checklists: For various study designs.
Assess the risk of bias independently by two or more reviewers. Resolve any disagreements through discussion or consultation with a third reviewer.
6. Synthesizing the Evidence
Evidence synthesis involves summarizing and integrating the findings of the included studies. This can be done narratively or statistically (meta-analysis).
- Narrative synthesis: A descriptive summary of the findings, often used when studies are heterogeneous or when a meta-analysis is not possible. Organize the synthesis around key themes or concepts.
- Meta-analysis: A statistical technique for combining the results of multiple studies to obtain an overall estimate of effect. Consider the eligibility of studies for meta-analysis based on clinical and methodological homogeneity. Use appropriate statistical methods, such as fixed-effect or random-effects models. Assess for publication bias using funnel plots and statistical tests (e.g., Egger’s test).
Alt text: A funnel plot visually represents publication bias in meta-analysis, plotting effect size against a measure of precision. Asymmetrical patterns may indicate bias.
7. Writing the Systematic Literature Review
The SLR report should clearly and concisely describe the methods, results, and conclusions of your review. Follow established reporting guidelines, such as the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) statement.
The report typically includes the following sections:
- Introduction: Background information, rationale for the review, and research question.
- Methods: Detailed description of the search strategy, inclusion/exclusion criteria, data extraction process, quality assessment methods, and synthesis methods.
- Results: Presentation of the findings, including the number of studies included, characteristics of the studies, and results of the synthesis.
- Discussion: Interpretation of the findings, limitations of the review, implications for future research, and conclusions.
- Conclusion: Summary of the main findings and their significance.
8. Addressing Potential Biases
Throughout the SLR process, it is crucial to be aware of potential biases that could influence the results. These biases can arise at various stages, including:
- Selection bias: Occurs when the selection of studies for inclusion is not random or representative.
- Publication bias: The tendency for studies with positive results to be more likely to be published than studies with negative results.
- Reporting bias: The selective reporting of outcomes within studies.
- Confirmation bias: The tendency to favor evidence that confirms pre-existing beliefs.
Employ strategies to minimize bias, such as using a comprehensive search strategy, having multiple reviewers, and using validated quality assessment tools.
9. Keeping the Review Updated
The body of evidence is constantly evolving. To ensure that your SLR remains relevant and up-to-date, consider periodically updating it. This involves repeating the search strategy, screening new articles, and updating the synthesis.
A standalone systematic literature review, when conducted rigorously, offers a valuable contribution to the knowledge base. By following the steps outlined in this guide, researchers can conduct comprehensive and transparent reviews that inform practice, policy, and future research.
