Start the search process by identifying the major concepts in your topic or research question. Think of these as the most important aspects - they are usually the nouns in your research question, such as people or populations, issues, or places.
In the health sciences, you can use the PICO Framework to identify the main concepts in a clinical question:
|PICO Framework Item||Example|
|P||Patient, problem, or population||
|C||Comparison or control (optional)||
Research question: Does exercise reduce heart attacks among people with heart disease?
Main concepts: people with heart disease (population), exercise (intervention), heart attacks (outcome)
Next, for each of your main concepts, choose several words or phrases that represent it - these will be your search terms. It's important to come up with alternatives, since there are many ways to refer to a concept. If you only use one, you may miss relevant articles.
There are two different types of search terms you can use: subject headings and keywords. For a comprehensive search, always use both:
|Type of Search Term||Description||How Do You Choose Them?|
Searching using preassigned terms representing topics or subjects for articles that have been "tagged" or labeled with that term.
Each database uses its own subject headings. OVID Medline's are called MeSH. The subject headings are organized in a hierarchical tree.
|Keyword (also known as "textword")||
Searching the "record" of a database for the presence of specific words or phrases you choose yourself. The record does not include the full-text of the article. The search will usually check the title, abstract, and author-provided keywords, but you can specify the fields you want to search.
|Concept||Subject Heading (MeSH)||Keywords|
|Heart disease||Heart diseases||
|Heart attack||Myocardial infarction||
Tip: Sometimes, the subject heading and keywords for a concept will be the same. Other times they won't match. It depends on the subject headings used by the database.
Once you've chosen your search terms, you're ready to combine them to create your search strategy.
Terms are combined using Boolean operators. They are a set of commands that search engines, online catalogues, and databases are able to understand. They also make searching more efficient by letting you combine dozens of queries into one search.
Boolean operators include: AND, OR, NOT, parentheses, truncation, and phrases
Need more help? See our page on Boolean operators.
AND tells the search engine to only return results that contain all the words you've entered. Since the search is more specific and selective, you'll retrieve fewer results.
Example: emotional bonding AND emotion regulation AND children
NOT tells the search engine to give you results that contain all of the words you entered except the word following NOT.
Example: smoking NOT cigars
OR tells the search engine to give your results that contain any of the terms you've entered. This creates a broader search, so you'll retrieve a greater number of results.
Example: woman OR women OR female
Truncation (usually represented by an asterisk *) allows you to search for multiple endings of the same root word.
Example: nutrit* = nutrition, nutritious, nutrient, nutrients, nutritionist
Search for two or more words as a unit by putting them in quotation marks. This is especially useful for titles or phrases.
Example: "sex differences"
By using parentheses, you can ask a search engine to perform several Boolean searches at the same time. The search engine will perform the search enclosed in parentheses first, before moving on to the other search terms.
Example: urbanization AND (England OR Britain) and ("20th century" OR "twentieth century")
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