How do Boolean operators work in literature searching?

AND narrows a search by requiring both terms (anxiety AND students); OR broadens it by accepting either, useful for synonyms (adolescents OR teenagers); NOT excludes a term. You typically OR together synonyms within a concept, then AND the concepts together.

Which databases should I search?

Use the databases central to your field — for example PubMed/MEDLINE and CINAHL in health, PsycINFO in psychology, ERIC in education, Scopus and Web of Science for multidisciplinary coverage. Search at least two so you don't miss field-specific work, and record each one.

What are inclusion and exclusion criteria?

They define what counts as relevant — for example publication years, study designs, populations, languages, and peer-reviewed vs grey literature. Setting them before you screen keeps selection systematic and defensible rather than driven by whatever you happen to find.

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How to build a literature search strategy

Q: What is a literature search strategy?

A search strategy is a documented, reproducible plan for finding the relevant literature: which databases you'll search, the keywords and synonyms drawn from your question, how you combine them with Boolean operators, and the inclusion and exclusion criteria you apply. Recording it lets others reproduce your search and is required for systematic reviews.

By Dr. Rafiq Muhammad, MD, PhD · Updated June 2026

A search strategy is the documented, reproducible plan for finding your literature — the databases you’ll search, the keywords drawn from your question, how you combine them with Boolean operators, and the criteria for what’s in or out. Writing it down is what turns “I googled around” into a defensible search a reader (or examiner) can trust and reproduce.

Four moves

Break the question into concepts. Most questions have 2–3 core concepts (e.g. anxiety, university students, mindfulness). Frameworks like PICO or SPIDER help.
List synonyms for each concept. “University students” → students, undergraduates, college, tertiary. Missing synonyms is the #1 reason searches miss key papers.
Combine with Boolean. OR within a concept (synonyms), AND between concepts, NOT to exclude.
Set inclusion/exclusion criteria. Years, designs, populations, languages, peer-reviewed vs grey — before you screen.

Example search: (anxiety OR stress) AND (undergraduate* OR "university student*") AND (mindfulness OR meditation) — synonyms OR’d inside each concept, concepts AND’d together. The * is a truncation wildcard (student* = student, students).

Where to search, and what to record

At least two databases relevant to your field (e.g. PubMed/MEDLINE, CINAHL, PsycINFO, ERIC, Scopus, Web of Science).
Record each search — database, exact string, date, and hits — in a search log. Systematic reviews require this.
Don’t forget reference-list (“backward”) and citation (“forward”) chasing, and key journals/grey literature.

Doing a systematic review? You’ll report your hits and exclusions in a PRISMA flow diagram — and the Lit-Review Readiness Check confirms your search and criteria are in place before you write.

Get the free Literature Review toolkit

A search-log template, a synonyms/Boolean worksheet, and inclusion-criteria checklist from Literature Review Simplified. We’ll email you the download link.

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Frequently asked questions

What is a search strategy?

A documented, reproducible plan: databases, keywords/synonyms, Boolean combinations, and inclusion/exclusion criteria.

How do Boolean operators work?

AND narrows (both terms), OR broadens (synonyms), NOT excludes. OR within a concept, AND between concepts.

Which databases?

At least two relevant to your field (PubMed, CINAHL, PsycINFO, ERIC, Scopus, Web of Science…), each recorded.

What are inclusion/exclusion criteria?

Rules for what counts — years, designs, populations, languages — set before screening to keep selection systematic.

The synthesis matrix → Is my review ready? →