Systematic Literature Review (PRISMA)
Overview
A systematic review uses explicit, pre-defined methods to identify, select, appraise, and synthesize all relevant research on a specific question. Unlike narrative reviews, systematic reviews follow a reproducible protocol that minimizes bias in study selection and interpretation. The PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) framework provides the standard reporting structure, including the iconic flow diagram tracking records through identification, screening, eligibility, and inclusion.
When to Use
- Synthesizing the totality of evidence on a well-defined research question
- Identifying gaps, contradictions, or consensus in a body of literature
- Establishing what is known before designing new empirical research
- Informing policy or practice guidelines with evidence-based synthesis
When NOT to Use
- When the research question is too broad to define clear inclusion criteria
- When a scoping review (mapping the landscape) is more appropriate than a systematic review (answering a specific question)
- When time constraints prevent the rigorous protocol required
- When there is very little published research on the topic (consider a scoping review first)
Assumptions
IRON LAW: A systematic review must be REPRODUCIBLE — every search
decision, inclusion criterion, and quality assessment must be documented
so another researcher can replicate the process. If your review cannot
be replicated, it is a narrative review, NOT a systematic review.
Key assumptions:
- Transparency and reproducibility distinguish systematic from narrative reviews
- A pre-registered protocol reduces bias in study selection and analysis
- At least two independent reviewers should screen and assess studies to reduce subjective bias
- Quality assessment of included studies is mandatory — not all evidence is equal
Methodology
Step 1: Define the Research Question and Protocol
Formulate a focused question using a framework (PICO for interventions, PEO for qualitative, SPIDER for mixed methods). Register the protocol (e.g., PROSPERO). Define databases, search terms, date ranges, and language restrictions.
| Framework | Components |
|---|
| PICO | Population, Intervention, Comparison, Outcome |
| PEO | Population, Exposure, Outcome |
| SPIDER | Sample, Phenomenon of Interest, Design, Evaluation, Research type |
Step 2: Execute the Search Strategy
Search at least 3 databases (e.g., Scopus, Web of Science, PubMed). Use Boolean operators (AND, OR, NOT) with controlled vocabulary and free-text terms. Document every search string and date. Supplement with citation chaining (forward and backward), grey literature, and hand-searching key journals.
Step 3: Screen and Select Studies
Apply inclusion/exclusion criteria in two phases:
- Title and abstract screening — two reviewers independently; resolve disagreements by discussion or third reviewer
- Full-text screening — apply criteria to full papers; record reasons for exclusion
Document the process in a PRISMA flow diagram:
- Records identified → duplicates removed → screened → eligible → included
Step 4: Extract Data, Assess Quality, and Synthesize
Extract data into a standardized form. Assess quality using appropriate tools (e.g., Cochrane RoB for RCTs, CASP for qualitative, JBI checklists). Synthesize via meta-analysis (quantitative), thematic synthesis (qualitative), or narrative synthesis. Report per PRISMA 2020 checklist.
Output Format
markdown
## Systematic Review: [Research Question]
### Protocol
- Question framework: [PICO/PEO/SPIDER]
- Registration: [PROSPERO ID or equivalent]
- Databases searched: [list]
- Date range: [start-end]
### Search Strategy
|----------|--------------|---------------|
| [name] | [Boolean query] | [N] |
### PRISMA Flow
- Identified: [N] records
- Duplicates removed: [N]
- Screened (title/abstract): [N]
- Excluded at screening: [N]
- Full-text assessed: [N]
- Excluded at full-text: [N] (reasons: ...)
- Included in synthesis: [N]
### Inclusion/Exclusion Criteria
|-----------|---------|---------|
| Population | [specification] | [specification] |
| Study type | [specification] | [specification] |
| Language | [specification] | [specification] |
| Date | [specification] | [specification] |
### Quality Assessment Summary
|-------|-----------|---------------|--------------|
| [author, year] | [RoB/CASP/JBI] | [high/moderate/low] | [specific issues] |
### Synthesis
- [Key finding 1 with evidence strength]
- [Key finding 2 with evidence strength]
- Gaps identified: [what remains unknown]
### Limitations
- [Search limitations]
- [Assessment limitations]
Gotchas
- A systematic review without a PRISMA flow diagram is incomplete — the flow diagram is not optional
- Pre-registering the protocol prevents post-hoc changes to inclusion criteria that introduce bias
- Grey literature (theses, conference papers, reports) must be considered to reduce publication bias
- Quality assessment is NOT pass/fail — it informs how much weight to give each study in the synthesis
- Do NOT conflate systematic review with meta-analysis; meta-analysis (statistical pooling) is one possible synthesis method within a systematic review
- Inter-rater reliability for screening and quality assessment should be reported (e.g., Cohen's kappa)
References
- Page, M. J., et al. (2021). The PRISMA 2020 statement: An updated guideline for reporting systematic reviews. BMJ, 372, n71.
- Higgins, J. P. T., et al. (Eds.). (2023). Cochrane Handbook for Systematic Reviews of Interventions (Version 6.4). Cochrane.
- Booth, A., Sutton, A., & Papaioannou, D. (2016). Systematic Approaches to a Successful Literature Review (2nd ed.). Sage.