If secondary literature is inadequate, conflicting, or questions remain, search the primary literature for additional evidence

The type of question informs the type of study you want to look for...

Therapy  - RCT | Cohort Study | Case Control Study | Case Series

Diagnosis  - Prospective Study - blind comparison to a gold standard | Cross-Sectional Study

Etiology/Harm - RCT | Cohort Study | Case Control Study |  Case Series

Prognosis - Cohort Study | Case Control Study | Case Series

Prevention - RCT | Cohort Study | Case Control Study | Case Series

Develop your search strategy - use PICO concepts to craft search statements.

Create one search statement to represent each concept; be specific; consider synonyms or more specific or broader terms.

Use Boolean operators to combine search statement in various ways.

Apply appropriate limits (dates, language, publication types, etc.)

Save the best citations from each set of results;

Refine the search strategy as you go.

Search is an iterative process. Continue searching as long as you still find new literature.