A health sciences literature review needs a range, not a fixed count; method and scope set the final tally.
Why The Count Depends On Purpose
Readers come with different goals. A quick assignment aims to map core findings. A dissertation chapter must argue a position with depth. A systematic review follows a protocol to capture all eligible evidence. Each path sets a different ceiling for the number of studies you include. In short, you choose a number that serves your question and your method.
Fast Orientation: Typical Ranges By Task
You want numbers you can act on. Here are working ranges many supervisors accept in health programs, assuming peer reviewed sources and a clear synthesis plan. Treat them as targets to plan your search, not rigid quotas.
| Context | Typical Word Count | Suggested Sources Range |
|---|---|---|
| Short Coursework Review | < 5,000 | 20–40 |
| Capstone Or Honors Project | 5,000–8,000 | 30–60 |
| Master’s Thesis Chapter | 8,000–15,000 | 40–80 |
| Doctoral Thesis Chapter | > 15,000 | 80–150+ |
| Systematic Review (Intervention) | Protocol Driven | Often 5–40 studies |
| Scoping Review | Protocol Driven | 100–300+ records |
What Shapes The Right Number
Scope. Narrow questions shrink the pool. Tight PICO elements or specific populations will lower the final tally. Broad umbrella topics quickly snowball and need strong limits.
Study Design. Reviews that prize randomized trials often include fewer studies than mixed method reviews of service delivery or prevalence.
Academic Level. Upper undergrad modules tend to expect dozens, not hundreds. Master’s and doctoral work often push into larger bodies of literature.
Word Budget. Text space controls how much evidence you can summarize with clarity. The longer the chapter, the more studies you can synthesize without turning into a list.
Time And Databases. A search that covers MEDLINE, Embase, CINAHL, PsycINFO, and trial registries will likely return more eligible studies than a two database pass.
How Many Sources Belong In A Health Sciences Review: Practical Ranges
When students ask “how many sources belong in a health sciences review,” they often mean “what range helps me pass with confidence.” Use this practical band: for taught modules and capstone projects, aim for roughly two to three dozen strong items. For a master’s thesis chapter, plan for several dozen more, and for doctoral work, plan for many dozens and up.
Why There Is No Single Magic Number
Evidence syntheses are built to be transparent, not to hit a quota. Methods like PRISMA 2020 lay out how to select and report studies, but they do not set a target count. Good reviews include every eligible study they can find inside the defined criteria, even if that means a small pool. Weak reviews cherry pick to reach a round number. Aim for fit, not optics.
What Authoritative Guides Emphasize
Reporting guidance stresses clarity over size. The PRISMA site asks you to document how many records you found, screened, included, and excluded, plus your reasons. The Cochrane Handbook urges sensitive searches and clear selection steps, not a fixed tally. Both are widely used across medical and health programs. They set shared expectations for clear, reproducible reporting.
Health Review Types And Typical Volumes
Narrative reviews that scope practice questions often synthesize a few dozen studies, mixing trials, observational work, and policy reports. Scoping reviews can grow far larger because they chart everything relevant. Intervention focused systematic reviews may include a modest set of trials, especially with strict PICO limits, while reviews of service models or risk factors often include many more observational papers.
How To Set A Target You Can Defend
Start with your question. Define the population, exposure or intervention, comparator, and outcomes in plain terms. Pre write inclusion and exclusion rules. Run pilot searches in the key databases. Scan the first two hundred hits for signal. Based on that scoping pass, set a planning range and document why. As you screen full texts, adjust the range. Keep a log so your final count has a clear audit trail.
Placing A Number On Coursework Reviews
Shorter coursework needs enough breadth to map themes without drowning the reader. For review sections under five thousand words, many programs accept twenty to forty substantive sources, provided they are recent, credible, and synthesized into themes rather than listed. That range lets you build a timeline of findings and carve out a gap for your own study without losing the thread.
Setting Expectations For Theses
A master’s chapter usually runs longer and must persuade the examiner that you understand the field end to end. That often means forty to eighty well chosen sources in the main synthesis, with methods notes and historical anchors in footnotes or side notes if your template allows. Doctoral reviews go deeper and wider. Many programs expect well over one hundred items across the chapter and annexed reading notes.
What About Systematic Reviews In Health
These projects follow a protocol, register a plan, and then include every eligible study found. Counts vary from a handful of trials to many hundreds of reports. One analysis of Cochrane reviews reported a typical review including about half a dozen trials. Newer audits show wide ranges across topics, with some fields still seeing small pools and others returning dozens of trials or very large observational datasets. The point stands: the method, not a quota, drives your final number.
Placing Authoritative Anchors
If you need an external rule to cite in your methods, rely on reporting guidance and method handbooks rather than blog targets. Link to the PRISMA flow diagram for your counts and to the Cochrane search and selection chapter for search steps. Those anchors reassure examiners that your process is sound, no matter whether your pool ends up at fifteen studies or one hundred and fifty.
Building A Mix Of Study Types
Health topics often cross designs. Map what you need early. If you are sizing a safety question for an intervention, trials and large cohort studies will carry the weight. For service delivery or workforce models, qualitative syntheses and mixed methods may be central. For prevalence, expect many cross sectional studies. Your mix affects volume, as some designs are rarer in niche clinical populations.
Quality Beats Quantity
Two dozen rigorous studies can move a field more than a hundred thin ones. Use risk of bias tools fit for your designs. Pair summary tables with clear paragraph level synthesis so readers can see how the evidence aligns across populations, settings, and measures. Cut weak or off topic items, even if that lowers your final tally. Depth of synthesis earns marks; long lists do not.
A Practical Workflow That Scales
Stage one: scoping. Frame a tight question and test a pilot search. Stage two: screening. Deduplicate, then screen titles, abstracts, and full texts. Stage three: extraction and appraisal. Capture features and judge bias with the right tool. Stage four: synthesis. Group by concept and outcome.
Signals That You Have Enough
Themes repeat across independent teams and settings. New hits add nuance, not new themes. Your risk of bias table fills with consistent judgments. Your funnel of study designs suits the question. You can explain why excluded items stayed out. When those signals appear, you likely have a defensible pool, even if the raw number looks small beside a friend’s topic.
Where To Put Historical Or Peripheral Sources
Keep the core synthesis tight. Park background items in a short context paragraph or in a brief separate subsection. If your field changed measurement tools over time, keep legacy items only when they illuminate shifts that matter for your outcomes. Trim the rest so your count reflects current practice or best available designs.
How To Talk About Your Final Count
Report search dates, databases, and registers. Show your flow diagram with counts at each step. Give plain reasons for exclusion. State included studies and reports, plus any ongoing items. Explain how you grouped studies to keep the synthesis readable.
| Review Type | Common Volume Band | Method Notes |
|---|---|---|
| Narrative Review | 20–60 studies | Theme based synthesis across designs |
| Systematic Review | 5–100+ studies | Protocol, registration, PRISMA reporting |
| Scoping Review | 100–300+ records | Maps evidence; breadth over depth |
| Prevalence Review | Dozens to hundreds | Many cross sectional datasets |
| Qualitative Synthesis | 10–50 studies | Focus on concept saturation |
Common Pitfalls That Inflate Or Deflate Counts
Over broad questions pull in mountains of noise. Over narrow filters cut out relevant designs. Poor deduping fakes a big pool. Vague inclusion rules make screening inconsistent. Listing study by study without synthesis adds bulk but not insight. Skipping a librarian led search misses key trials or registries and weakens your claim to completeness.
A Safe Way To Phrase Your Method
State that you aimed to identify all eligible studies that match predefined criteria within set databases and registries and that you followed transparent reporting using the PRISMA 2020 checklist. This wording frames your count as the output of a method, not the target of one.
Quick Answers To Popular “How Many” Scenarios
Short coursework review in health programs: plan for twenty to forty high value sources. Large capstone or honors project: plan for thirty to sixty. Master’s chapter: plan for forty to eighty. Doctoral chapter: expect many dozens across the main text and annexes. Intervention focused systematic reviews: can be under ten trials in niche topics or several dozen in mature areas. Scoping reviews: often hundreds.
Final Tip: Aim For Fit, Then Prove It
Pick a range that your question, search, and word budget can carry. Keep your log tidy, your tables lean, and your synthesis crisp. When the pool looks defensible and the story reads clean, you have the right number.