CINAHL is the Cumulative Index to Nursing and Allied Health Literature, and for any review touching nursing, midwifery, physiotherapy, occupational therapy, or speech and language work it is not optional. It indexes journals MEDLINE does not carry, and it uses its own thesaurus, CINAHL Subject Headings, which overlaps with MeSH but is not a copy of it. A search translated across without adjusting the vocabulary will silently lose records.

Why the overlap argument is wrong

Reviewers sometimes argue that CINAHL is redundant because most of its content also sits in MEDLINE. The unique-yield question has been examined repeatedly and the answer depends entirely on topic. For a drug intervention the unique contribution may be small. For anything concerning nursing practice, care delivery, patient education, or the allied health professions, CINAHL carries material indexed nowhere else, including dissertations, practice guidelines, and journals below the indexing threshold of the larger databases.

The methodological point is that you cannot know the unique yield in advance for your topic, and omitting a database because it probably adds little is not a defensible position in a protocol. Our guide to choosing databases covers how to justify the set you searched.

Subject headings are not MeSH

The single largest source of error in translated searches is assuming the two thesauri align. They frequently do not.

Terms exist in one and not the other. Where a term exists in both, its scope note may differ, so the same string retrieves a different set. Hierarchies diverge, which matters enormously because exploding a term pulls in everything beneath it, and what sits beneath a heading is not the same in the two systems.

The practical consequence is that every concept block has to be rebuilt against the CINAHL thesaurus rather than pasted across. Look each concept up, read the scope note, check what explodes underneath, and record the decision. The background on how controlled vocabulary works is in subject headings and thesauri.

Syntax that behaves differently

  • Subject heading marker. CINAHL uses MH for exact headings and MM for major concept headings. There is no MeSH-style bracket syntax.
  • Explosion is not automatic. A heading does not explode unless you ask it to, which is the reverse of some interfaces and a frequent cause of undercounting.
  • Truncation and wildcards. The asterisk truncates and the hash and question mark handle internal variation. Spelling variation between American and British usage matters more in nursing literature than in clinical trials.
  • Proximity. CINAHL supports N for near, which is often more precise than a broad Boolean AND across a full record. See Boolean and proximity operators.

Filters, and why to be careful with them

CINAHL offers tempting limiters: peer reviewed, research article, evidence-based practice, and a set of publication-type filters. They are applied to indexed metadata, and metadata is incomplete. Restricting to research articles can drop relevant studies whose record was never tagged.

The defensible pattern is to avoid interface limiters in the main search and apply eligibility at screening, where a human is making the judgement and the decision is recorded. Where a limiter is used it belongs in the reported strategy, because it changes what the search could have found.

Reporting it so someone can rerun it

The strategy has to be reproducible: the platform, the exact line-by-line search with the operators as entered, the date the search was run, any limiters, and the yield at each step. Platform matters because CINAHL behaves differently across host interfaces, and a strategy that runs in one may error in another.

Before running the final version, have the strategy checked. Peer review of the search using the PRESS checklist catches the errors that are invisible from inside, and documenting the search sets out exactly what to record.