Systematic Review and Meta-Analysis with PRISMA
How to conduct and report a systematic review, protocol, search strategy, screening, PRISMA flow diagram, and when meta-analysis is appropriate.
A systematic review answers a focused question by finding, appraising and synthesising all relevant studies using an explicit, reproducible method. Meta-analysis goes further, statistically combining results. Both sit near the top of the evidence hierarchy, and both are judged on the transparency of their method, for which PRISMA is the reporting standard.
Start with a Protocol and a Focused Question
Systematic reviews are pre-planned. Register a protocol (e.g. PROSPERO for health reviews) before you begin, to guard against selective reporting. Frame the question with a structured format such as PICO (Population, Intervention, Comparison, Outcome), which also drives your search terms and inclusion criteria.
Search Strategy
Search comprehensively across multiple databases (e.g. MEDLINE, Embase, CINAHL, Cochrane), using a documented combination of keywords and controlled vocabulary (MeSH). The search must be reproducible: report the exact strings and dates so another team could repeat it. Supplement with reference-list and citation searching.
Screening and Selection
Apply pre-set inclusion and exclusion criteria in two stages, title/abstract, then full text, ideally with two independent reviewers to reduce bias. Record numbers at each stage for the PRISMA flow diagram, which shows records identified, screened, excluded (with reasons) and finally included.
Quality Appraisal
Assess the risk of bias in each included study using an appropriate tool (e.g. Cochrane RoB 2 for trials, Newcastle-Ottawa for observational studies). The strength of your conclusions depends on the quality of the underlying evidence, so this step is not optional.
Synthesis: Narrative or Meta-Analysis
If studies are too heterogeneous to combine statistically, synthesise narratively around themes. If they are sufficiently similar in design, population and outcome, meta-analysis pools effect sizes, typically presented in a forest plot, and quantifies heterogeneity (e.g. the I² statistic). Do not force a meta-analysis onto incompatible studies. A misleading pooled estimate is worse than an honest narrative synthesis.
Review Types, and Which You Are Actually Doing
Students frequently label a piece a systematic review when the brief asked for something lighter. The distinction matters, because a systematic review makes a claim about completeness that you must then evidence.
| Type | Search | Appraisal | Typical use |
|---|---|---|---|
| Narrative review | Selective, not exhaustive | Informal | Undergraduate essays, background chapters |
| Scoping review | Broad, mapping the field | Usually none | Establishing what evidence exists |
| Systematic review | Exhaustive, documented, reproducible | Formal risk-of-bias tool | Postgraduate dissertations, publication |
| Meta-analysis | As systematic review | As systematic review, plus statistical pooling | Where studies are similar enough to combine |
| Rapid review | Systematic method, deliberately limited | Often simplified | Time-constrained work, stated as a limitation |
If you cannot document the search well enough that another person could repeat it and get your result, you have written a narrative review. Say so. Calling it systematic when it is not is the fastest way to lose credibility with an examiner.
PRISMA and Where It Fits
PRISMA stands for Preferred Reporting Items for Systematic Reviews and Meta-Analyses. It is a reporting guideline, not a method: it tells you what to disclose, not how to conduct the review. The current version is PRISMA 2020, published in the BMJ, and it is indexed alongside other reporting standards by the EQUATOR Network.
Two components matter for student work. The checklist lists the items your write-up must contain. The flow diagram shows how many records you identified, screened, excluded and included, with reasons for exclusion at full-text stage. Markers look for the diagram first, because it reveals instantly whether the process was systematic.
Framing the Question
| Framework | Elements | Best for |
|---|---|---|
| PICO | Population, Intervention, Comparison, Outcome | Clinical effectiveness questions |
| PICOS | PICO plus Study design | Where you restrict to trials or cohorts |
| SPIDER | Sample, Phenomenon of Interest, Design, Evaluation, Research type | Qualitative evidence synthesis |
| SPICE | Setting, Perspective, Intervention, Comparison, Evaluation | Social science and service evaluation |
The framework does more than shape the question. Each element becomes a concept block in your search string, so choosing it early saves rework.
Building a Search You Can Defend
The search is where most student reviews come apart, and it is also the part a marker can check most easily. Build it in layers.
- Split the question into concept blocks. Each element of your framework becomes one block.
- Gather synonyms within each block and join them with OR, including British and American spellings.
- Join the blocks with AND. Fewer blocks means more results. Three is usually the practical maximum.
- Add controlled vocabulary such as MeSH terms in MEDLINE, alongside your free-text terms rather than instead of them.
- Record the string, the database and the date every time you run it. Databases change, so an undated search is unreproducible.
Then supplement the database search. Check the reference lists of your included studies, look at what has cited them since, and search relevant grey literature such as theses and government reports. Reporting these steps signals a serious method.
Risk of Bias Tools by Study Design
| Study design | Common tool |
|---|---|
| Randomised trials | Cochrane RoB 2 |
| Non-randomised interventions | ROBINS-I |
| Observational, cohort or case-control | Newcastle-Ottawa Scale |
| Qualitative studies | CASP qualitative checklist |
| Mixed study types | Mixed Methods Appraisal Tool |
Name the tool you used and report the result per study, usually as a table. "Studies were of good quality" without a tool or a table is an assertion, not an appraisal.
Narrative Synthesis Versus Meta-Analysis
Meta-analysis is not the more impressive option. It is the appropriate option only when studies are similar enough in population, intervention and outcome measure to combine meaningfully.
- Combine when designs and outcome measures align, reporting a forest plot and a heterogeneity statistic such as I².
- Do not combine when populations, interventions or outcomes differ materially. Synthesise narratively around themes instead.
- Say why. Examiners want the reasoning, and a stated decision not to pool demonstrates judgement.
A misleading pooled estimate is worse than an honest narrative synthesis, because it puts a number on a comparison that was never valid.
Common Mistakes and Fixes
| Mistake | Fix |
|---|---|
| Search string not reported | Reproduce the exact string per database, with the date run, in an appendix |
| One database only | Search at least three relevant databases plus reference lists |
| No exclusion reasons at full-text stage | PRISMA requires them. Record as you screen, not afterwards |
| Screening alone with no check | Have a second screener on a sample and report the agreement |
| Calling a narrative review systematic | Describe what you actually did and name the limitation |
| Pooling incompatible studies | Synthesise narratively and explain the heterogeneity |
Discipline Notes
- Health and medicine: PRISMA is expected, and protocol registration on PROSPERO is standard practice.
- Nursing and allied health: CINAHL joins MEDLINE and Embase as a core database.
- Education and social sciences: ERIC and Scopus matter, and qualitative synthesis frameworks such as SPIDER often fit better than PICO.
- Computing and engineering: systematic reviews follow the same logic, but IEEE Xplore and ACM replace the health databases.
- Undergraduate work everywhere: a full systematic review is rarely expected. A systematic search reported transparently usually is.
Where Ethical Support Fits
A librarian will help build and document your search strategy, and that is exactly the sort of support universities provide for this. Statistical advice on whether pooling is appropriate is also legitimate. What stays yours is screening the studies, appraising them and deciding what the evidence shows.
Frequently Asked Questions
Do I have to register a protocol?
For a student dissertation, usually not, though it is good practice and some supervisors require it. For anything intended for publication in health research, expect to.
How many studies should a systematic review include?
There is no target. The number is whatever meets your criteria. A review finding four eligible studies is a valid result, and the scarcity is itself a finding.
Can I do a systematic review alone?
Student reviews are often solo. Acknowledge single-screener bias as a limitation, and where possible have someone check a sample of your screening decisions.
What is I² telling me?
It estimates the proportion of variation across studies due to heterogeneity rather than chance. High values suggest the studies may not belong in one pooled estimate.
Do I need meta-analysis for a good mark?
No. Marks come from method transparency and appraisal quality. A well-justified narrative synthesis beats an inappropriate pooled estimate.
Your Next Step Today
Open the PRISMA 2020 checklist and mark which items your draft already reports. The gaps are your task list, and they are usually search documentation and exclusion reasons.
Checklist
- Was a protocol registered and a focused question set using a suitable framework?
- Is the search reproducible, with strings and dates reported?
- Was screening against pre-set criteria, with exclusion reasons recorded?
- Is risk of bias appraised with a named tool and reported per study?
- Is the synthesis method justified rather than assumed?
- Is a PRISMA flow diagram included?
Trusted Sources
- Page MJ and others, The PRISMA 2020 statement: an updated guideline for reporting systematic reviews, BMJ 2021. Open access. Accessed 11 August 2026.
- PRISMA statement website, checklists and flow diagram templates. Accessed 11 August 2026.
- EQUATOR Network, the index of reporting guidelines across study types. Accessed 11 August 2026.
- Paré G and Kitsiou S, Methods for Literature Reviews, NCBI Bookshelf, on review typologies. Accessed 11 August 2026.
- Louisiana State University Libraries, Steps in a systematic review, practical workflow. Accessed 11 August 2026.
Review requirements differ by discipline and by supervisor. Where this guide and your department's guidance differ, follow your department.
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