Medical Literature Review

Finding, comparing and appraising scientific sources.

A medical literature review is not simply the collection of everything published on a topic. Searching is the work of narrowing the question being asked; where the question is not sharp enough, the number of results rises while their usefulness falls.

An answerable question

Clinical questions are structured into four components: the patient or population, the intervention, the comparison, and the outcome measured. That structure reveals the search terms almost by itself.

Sources and differences in coverage

No single database covers the whole literature:

• PubMed / MEDLINE — the principal index of biomedical literature, with structured searching through MeSH terms.
• Cochrane — systematic reviews and registers of controlled trials.
• Trial registries — revealing studies that are ongoing or were never published.

The last matters for publication bias: studies with unfavourable results tend to be published later or not at all.

Documenting the search

For reproducibility, what must be recorded includes the databases used and the date of access, the full search string, limits by language and year, inclusion and exclusion criteria, and the number of records removed at each stage with the reason. The PRISMA flow diagram is widely used to report that process visibly.

From screening to appraisal

Screening on titles and abstracts is fast but error-prone, so exclusion criteria are best kept narrow at that stage. At full text, the methodological quality of each study is assessed separately.

A search that continues

Literature does not stand still. Where a topic continues to be followed, the search string should be retained and re-run at intervals, so that an update becomes the continuation of a recorded piece of work.