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HLTB15: Introduction to Health Research Methodology

Winter 2021

Main Concepts

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
  • Disease or health condition
  • Patient's demographics
  • Patient's risk factors
I Intervention
  • Exposure
  • Therapeutic measure (e.g. medication, surgical intervention, lifestyle change)
  • Preventative measure
  • Diagnostic test or procuedure
C Comparison or control (optional)
  • Standard care
  • Different intervention or preventative measure
  • Placebo
O Outcome
  • Measure of clinical wellbeing or quality of life (e.g. disease incidence, mortality rate, survival rate, rate of disease progression)


Research question: Does exercise reduce heart attacks among people with heart disease?

Main concepts: people with heart disease (population), exercise (intervention), heart attacks (outcome)

Search Terms

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?
Subject heading

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. 

  • Use a subject heading lookup tool (e.g. for PubMed or Medline, use the MeSH browser)
  • In OVID databases (e.g. Medline, Embase, PsycINFO), use the "map term to subject heading" feature
  • Look for a thesaurus or subject heading list in other databases
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.

  • For each main concept (PICO item), brainstorm a list of synonyms or related terms that represent or describe it
  • Consider scientific vs. common names, alternate spellings, singular and plural forms, different word forms (e.g. noun, adjective)


Concept Subject Heading (MeSH) Keywords
Heart disease Heart diseases
  • Heart disease(s)
  • Cardiac disease(s)
Exercise Exercise
  • Exercise
  • Physical activity
  • Training
Heart attack Myocardial infarction
  • Heart attack(s)
  • Myocardial infarct(s)
  • Myocardial infarction(s)

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. 

Search Strategies

Boolean Operators

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

Narrow Your Search: AND, NOT

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

Expand Your Search: OR, Truncation

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

Phrase Searching

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"

Combining Searches

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")

Troubleshooting Your Search

Too Many Results?

  • Add keywords to narrow your topic
  • Try searching by subject heading

Too Few Results?

  • Check the spelling of your keywords
  • Remove keywords to broaden your search