What is a Systematic Literature Review?

A systematic literature review is a structured, organized and transparent process for identifying, selecting, and critically appraising relevant research studies to answer a specific research question. Systematic reviews apply predefined criteria for selecting studies, assessing their quality, and synthesizing their findings. This rigorous methodology ensures that a literature review is exhaustive and reproducible.

At the heart of a systematic review lies a well-defined protocol that guides the entire process, from the formulation of research questions to the selection and appraisal of relevant studies. This systematic approach contrasts with other literature reviews, which may be conducted more flexibly.

The methods in a systematic literature review are designed to offer a comprehensive textual summary and synthesis of existing research, providing context and background information critical to understanding the broader research landscape. Systematic reviews are essential for informing evidence-based practices and policy decisions, as they consolidate findings from numerous studies and offer a high level of evidence.

A systematic review often follows specific guidelines such as the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) (Page et al., 2020). The guidelines ensure that reviews are conducted rigorously and reported clearly. This facilitates the replication of findings and the assessment of conclusions; while PRISMA primarily focuses on quantitative research, it has extensions like PRISMA-ScR that can apply to qualitative research. Researchers also use the Cochrane Handbook for Systematic Literature Reviews (Higgins et al., 2023) which focuses on detailed guidelines for doing systematic reviews of healthcare interventions.

When to conduct a systematic review?

Systematic reviews are often used in evidence-based research and practice, particularly in environmental science, healthcare, and social sciences. Researchers undertake these reviews to identify gaps in current evidence and suggest areas for further investigation. They are essential in developing guidelines and informing policies by providing nuanced and detailed evaluations of experiences, perceptions, and contextual factors.

Qualitative systematic reviews support grant applications by demonstrating the current state of qualitative knowledge and the need for further exploration. Organizations employ a systematic review methodology to improve practices and interventions. Public health professionals rely on qualitative systematic reviews to assess the effectiveness of interventions and shape strategies that consider the socio-cultural contexts. Regularly updating these reviews ensures that the synthesized qualitative evidence remains current, aiding in more informed and effective decision-making in various disciplines.

How do systematic literature reviews differ from other reviews?

Systematic literature reviews differ from other types of reviews in their methodology, scope, and rigour. They follow a structured approach with clear research questions, predefined criteria, comprehensive search strategies, and systematic data extraction. Other reviews, like narrative reviews, are more flexible and less structured, often lacking predefined criteria and systematic searches.

Systematic reviews aim to cover all relevant studies on a specific question. In contrast, other reviews may focus on a narrower study scope and include studies selectively, reflecting the author's perspective. Systematic reviews also employ a systematic search strategy to cover multiple databases and grey literature sources such as government or technical reports, reducing the risk of cherry-picking studies.

Rigor is another key difference. Systematic reviews critically appraise the quality of included studies and often use statistical methods (in the case of quantitative research) or thematic analysis to synthesize findings. Other reviews do not usually include formal quality assessments and rely more on narrative synthesis.

Reproducibility is a hallmark of systematic reviews. They document their process in detail, allowing others to replicate the study. Other reviews often lack this detailed methodology, making replication difficult and leading to potential inconsistencies.

Transparency is crucial in systematic reviews, with published protocols, documented search strategies, and clear study selection processes. Guidelines like the PRISMA checklist (Page et. al 2020) ensure thorough reporting. Other reviews do not usually follow strict guidelines and may not fully disclose their methods and criteria.

The primary objective of systematic reviews is to provide high-quality evidence, informing clinical practice, policy-making, and further research. Other reviews aim to offer overviews or summaries of the literature, providing insights and perspectives rather than systematic evidence synthesis.

How to conduct a systematic literature review?

To effectively conduct a systematic literature review, it is crucial to follow a structured set of instructions that encompass comprehensive planning, rigorous methodology, and meticulous documentation. The following steps are recommended when conducting a systematic literature review:

1. Define the research question: Clearly state the research question(s) you intend to answer, ensuring it is specific, open-ended, and suitable for detailed exploration. This will guide all subsequent steps. For example, "How do adolescents perceive the impact of social media on their mental health?" Break down the main question into sub-questions, such as: What are the positive and negative perceptions of social media among adolescents? How do adolescents describe their emotional responses to social media interactions? What coping strategies do adolescents use to manage social media-induced stress?

2. Develop a protocol: Outline the methodology and criteria for your review in a detailed protocol to ensure transparency. Include background information, rationales, and clearly stated objectives. Define inclusion and exclusion criteria based on the study population, context, data collection methods, and outcomes of interest. Identify and list the databases you will search, such as PubMed, PsycINFO, and Scopus. Develop keywords and search strings using Boolean operators. Create a data extraction form to capture relevant data from each study. Optionally, register your protocol with a platform like PROSPERO for enhanced transparency.

3. Conduct a comprehensive literature search: Perform a thorough search across identified databases using developed keywords and search strategy. Document the search process meticulously, including search dates, databases searched, and the number of records retrieved. This ensures a comprehensive capture of relevant studies related to your research question.

4. Screen and select studies: Apply the inclusion and exclusion criteria to filter studies. Start with an initial screening of titles and abstracts, followed by a full-text review of remaining studies for final inclusion. Document reasons for exclusion at each stage to ensure transparency and consistency.

5. Assess the quality of studies: Use standardized tools, such as the Critical Appraisal Skills Programme (CASP)for qualitative studies to assess the quality of qualitative studies. Evaluate aspects like credibility, transferability, dependability, and confirmability. Ensure consistency and document the process and outcomes.

6. Extract data: Develop a data extraction form to systematically capture relevant data from each included study, such as study design, participant characteristics, data collection methods, themes, and findings. Use qualitative data analysis software such as ATLAS.ti for coding and theme identification.

7. Analyze and synthesize data: Identify and synthesize key themes and patterns across studies. Conduct a meta-synthesis to integrate findings and provide a comprehensive understanding of the research question. Ensure a thorough synthesis to highlight variations and commonalities across studies.

8. Report findings: Follow a structured format including an introduction, methods, results, discussion, and conclusion. Adhere to PRISMA guidelines (Page et. al 2020) for transparent reporting. Use tables, figures, and flow diagrams to illustrate findings and the study selection process.

9. Discuss implications: Interpret the findings within the context of existing literature, acknowledging limitations and suggesting areas for future research. Provide recommendations based on gathered evidence.

10. Update and maintain the review: Consider periodic updates as new studies become available to ensure findings remain current. Set up database alerts to stay informed about new research.

Conclusion

A systematic literature review rigorously answers specific research questions by evaluating and synthesizing evidence from multiple studies, providing comprehensive context and background information. Unlike other literature reviews, systematic review protocols follow a structure with predefined criteria, ensuring exhaustive and reproducible results. They adhere to guidelines like PRISMA (Page et. al 2020) for thorough reporting and trustworthy conclusions. Systematic reviews are essential in healthcare and social sciences because they help identify evidence gaps and inform policies. Regular updates keep the evidence current, supporting effective decision-making across various disciplines.

References

1. Page M J, McKenzie J E, Bossuyt P M, Boutron I, Hoffmann T C, Mulrow C D et al. The PRISMA 2020 statement: an updated guideline for reporting systematic reviews BMJ 2021; 372 :n71 doi:10.1136/bmj.n71

2. Higgins JPT, Thomas J, Chandler J, Cumpston M, Li T, Page MJ, Welch VA (editors). Cochrane Handbook for Systematic Reviews of Interventions version 6.4 (updated August 2023). Cochrane, 2023.