Multi-database searching is not optional in a systematic review. Every major reporting guideline, including PRISMA and the Cochrane Handbook, requires searches across multiple bibliographic databases. PubMed covers approximately 30 million records but has limited coverage of conference proceedings, gray literature, and non-English journals. Embase captures broader European and pharmacological literature. Cochrane's CENTRAL indexes controlled trials not always found in PubMed. CINAHL covers nursing and allied health comprehensively.
The challenge is that each database uses a different controlled vocabulary and different syntax rules.
Try our free Database Search Translator to convert your PubMed search string automatically.
Why Direct Copy-Paste Fails
A typical PubMed search line uses MeSH (Medical Subject Headings) terms and free-text terms with field tags like [MeSH] and [tiab].
If you paste this into Embase, [MeSH] is not recognized. Embase uses Emtree with different term names and hierarchies. The [tiab] tag does not exist; Embase uses :ti,ab instead.
Running an untranslated string typically generates errors, retrieves zero results, or silently drops controlled vocabulary terms while retrieving only free-text matches.
MeSH vs Emtree: Key Differences
Some examples of term differences: Myocardial Infarction (MeSH) becomes heart infarction (Emtree). Neoplasms becomes neoplasm. In Embase, controlled terms use /exp for explosion: diabetes mellitus/exp.
Cochrane CENTRAL Syntax
MeSH descriptor: [term] explode all trees format. Field restrictions: :ti, :ab, :kw. Boolean operators must be capitalized.
CINAHL Syntax
Controlled vocabulary: (MH "term+") where + indicates explosion. Title and abstract: TI and AB, capitalized. Combined: TX for all text.
For building your initial strategy, see our Search Strategy Builder.
Step-by-Step Conversion
Step 1: Audit your PubMed search line by line. Separate MeSH terms, free-text, and filters.
Step 2: Replace MeSH terms with Emtree equivalents using the Emtree browser.
Step 3: Convert field tags.
| PubMed | Embase | Cochrane | CINAHL |
|---|---|---|---|
| [tiab] | :ti,ab | :ti,ab | TI or AB |
| [MeSH] | /exp | MeSH descriptor explode | (MH "term+") |
| [pt] | [it] | Publication Type: | (PT "type") |
Step 4: Check truncation and phrase syntax (all databases support * and double quotes).
Step 5: Reconstruct and test in each database.
Step 6: Document every search string, date, and result count.
Our Database Search Translator automates steps 2 through 4.
Common Translation Errors
Not exploding controlled terms (forgetting /exp in Embase or + in CINAHL). Using MeSH terms directly in Embase. Missing database-specific terms. Neglecting publication type filter translation.
For managing retrieved records, see our Inclusion/Exclusion Tool.
How Many Databases to Search
Minimum for health and biomedical reviews: PubMed, Embase, and Cochrane CENTRAL. Add CINAHL for nursing topics, PsycINFO for psychology, ERIC for education.
Key Takeaways
- Multi-database searching is required for systematic reviews; PubMed alone is insufficient.
- Each major database uses different controlled vocabulary and field tag syntax.
- MeSH terms must be converted to Emtree equivalents for Embase.
- Always explode controlled vocabulary terms using the correct modifier (/exp, +, explode all trees).
- Document every search string, date, and result count for transparent reporting.
- Our Database Search Translator automates the most time-consuming translation steps.
FAQ
Why can't I use the same search string in every database?
Each database uses different controlled vocabulary and syntax. An untranslated PubMed string will produce errors, partial results, or silently omit controlled vocabulary matches.
What is the difference between MeSH and Emtree?
MeSH is PubMed's controlled vocabulary (National Library of Medicine). Emtree is Embase's (Elsevier). Both organize biomedical concepts hierarchically but with different term names and scope.
How do I find the Emtree equivalent of a MeSH term?
Search the Emtree browser in the Embase interface. Our Database Search Translator handles common mappings automatically.
Do I need to search CINAHL for every systematic review?
Not every review, but it is essential for nursing, allied health, primary care, rehabilitation, and patient education topics.
How do I document searches for PRISMA reporting?
Record database name, interface, complete search string, date, and number of records retrieved. Present in a supplementary table per PRISMA 2020 checklist item S1.
My translated search retrieves far fewer results in Embase. What went wrong?
Check that all controlled terms use /exp, that Emtree terms are correct, and that field tags have been converted properly.
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