Boolean Operators: AND, OR, NOT

There are only three Boolean operators, and understanding them is the foundation of all database searching: OR — Use BETWEEN synonyms (within the same concept). OR broadens your search by finding articles that contain ANY of the terms. - Example: 'diabetes OR hyperglycemia OR high blood sugar' - Result: Articles containing any one of these terms are included - Think: casting a wider net AND — Use BETWEEN different concepts (different PICO elements). AND narrows your search by requiring articles to contain ALL terms. - Example: 'diabetes AND metformin' - Result: Only articles containing BOTH terms are included - Think: tightening the filter NOT — Use to EXCLUDE specific terms. Use sparingly — it can accidentally exclude relevant articles. - Example: 'diabetes NOT gestational' - Result: Removes articles mentioning gestational diabetes - Warning: An article about type 2 diabetes that also mentions gestational diabetes would be excluded. Use NOT with extreme caution. The correct Boolean structure for a PICO search: (P synonyms OR P synonyms OR P synonyms) AND (I synonyms OR I synonyms OR I synonyms) Critical rule: Use OR within a concept, AND between concepts. Parentheses group the OR terms together. The most common beginner mistake: Using AND between synonyms. 'Hypertension AND high blood pressure' finds only articles that contain BOTH terms — a tiny fraction. 'Hypertension OR high blood pressure' finds articles with EITHER term — a much larger and more complete set.