How to Search Literature for a Narrative Review

A narrative review search should be broad enough to capture the main evidence and transparent enough that readers understand how sources were found. It need not be exhaustive, but it must not be arbitrary.

A practical plan

1. Define concepts and synonyms from your aim.
2. Search at least two databases (for example PubMed and Embase or another relevant database).
3. Start with recent reviews and guidelines to find landmark studies and recent updates.
4. Use citation chasing (reference lists and "cited by").
5. Search for opposing views deliberately to reduce confirmation bias.
6. Record databases, dates, key search strings and the number of records screened.
7. State the limits: that the search was not exhaustive, and which languages and years were included.

Reducing selection bias

Selection bias is the main weakness of narrative reviews. Write down inclusion principles before searching (for example "randomised trials and cohort studies in adults, 2015–2026, English"), search for evidence that challenges your expectations, and have a colleague check your list of sources against theirs.

Illustrative example

Invented for teaching. A student searching for the role of vitamin D in respiratory infections finds that most abstracts support a benefit. She deliberately searches for null trials and meta-analyses with conflicting results, adds them, and reports the disagreement and possible reasons.

Checking for gaps in your search

Compare your reference list with the references of two recent, high-quality reviews on the topic. If key papers appear in theirs but not yours, find out why: a missing synonym, an unindexed journal or a different date range. Ask a mentor or librarian to run a quick check search. This small step greatly improves confidence that the search was reasonable.

Common pitfalls

• Searching only for studies that fit your view.
• Not recording the search.
• Relying on a single database.

Key takeaways

• Be broad, transparent and balanced.
• Record what you did and the limits of the search.

This page is general educational information about research methods. It is not medical, legal or regulatory advice; follow your institution's ethics board and your target journal's instructions.