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Clinical Essentials: Search

Literature search guide

Find health information strategically


Do a literature search: step-by-step



Question     Define your research question

Key concepts     Concentrate on the key concepts

Terms     Gather search terms

Search statement     Write the search statement

Databases     Search a database

Refine     Make search refinements


Step 1: Define your research question

Use the PICO mnemonic to frame a well-formed clinical question.

The research question lays the foundation for the literature search.


►  Determine the PICO components of your question


P Problem, Patient, and/or Population – Who is the patient or population?
– What is the problem, condition, or issue?
I Intervention or Exposure – What is the proposed treatment?
– What is the proposed test or procedure?
– What is the factor of interest?
C Comparison – Am I comparing with another intervention or exposure?
O Outcome – What do I hope to improve, measure, or accomplish?


Example PICO
Problem: heart attack
Intervention: aspirin
Comparison: other antiplatelet aggregators
Outcome: heart attack prevention


►  Frame the PICO question


Example PICO question

For patients with a history of heart attacks (P), is aspirin (I) more effective than other antiplatelet aggregators (C) in preventing further heart attacks (O)?


Use a template to frame your PICO question →


Step 2: Concentrate on the key concepts

Less is more.

Impose fewer restrictions to get more search results.


►  Focus on 2 or 3 ideas from your question



Start your search with these concepts:

Concept 1  Problem

Concept 2  Intervention


In general, the problem and intervention concepts are more clearly defined in the titles and abstracts of publications.


Step 3: Gather search terms

We can express the same idea using different words and phrases. 

If you include different terms with similar or related meanings in your search, you may find a broader range of results.


►  Collect terminology for each concept

Consider the following types of terms:


Types of terms Examples
Synonyms hypertension, high blood pressure
Abbreviations CO2, bp, ddx
Plurals viscus – viscera, femur – femora
Professional or research terms cerebrovascular accident for stroke
Slang or vernacular terms bounceback for readmission
Different spellings pediatrics – paediatrics (US & UK)
Related concepts cancer, malignancy, tumor


Try these additional ways for identifying search terms:

►  Consider other types of similar terms → 

►  Review background sources (like UpToDate or Wikipedia) to find more expressions.

►  Run a preliminary database search and examine the results for helpful language.


Example search terms

heart attack
myocardial infarction
heart infarction

Intervention: aspirin
acetylsalicylic acid


Step 4: Write the search statement

The search statement is the text entered into the search box.


►  Arrange your search terms in this pattern


Search statement template

(  __  OR  __  OR   __  )  AND  (  __  OR  __  OR   __  )


Fill in the blanks with
Concept #1 terms

Fill in the blanks with
Concept #2 terms


Add more search terms or concepts using the proper operator: OR, AND, or ( ).


Example search statement

(heart attack OR myocardial infarction OR heart infarction OR AMI OR MI) AND (aspirin OR acetylsalicylic acid OR ASA)


The search operators define the logical relationships between search terms. Here are the ways:

►  OR joins similar terms – such as synonyms and related concepts.

►  AND combines different concepts.

►  Parentheses ( ) group together similar terms into a conceptual unit.

Learn how search operators work →


Step 5: Search a database

Databases are searchable collections of information.

You have several database options for health literature searching.


►  Choose a database specializing in your topic

We recommend the following databases as starting points for your research.


  Databases for extensive searching

Use the following databases for a comprehensive literature search.

They are suitable for research projects.


Topic Area Databases
All health specialties PubMed All health topics. A popular database.
Embase All health topics. Specialized in pharmacology.
Psychiatry and psychology PsycInfo Behavioral and social sciences focus
Nursing and allied health CINAHL Nursing and allied health (OT, PT, RD, SLP) literature
Life sciences BIOSIS Biology, genetics, and basic health sciences focus
Multidisciplinary Web of Science

Google Scholar
Diverse research fields. Beneficial for multidisciplinary topics.

Find databases in other subject areas →


  Databases for summaries of research

Use the following databases to find reviews of research literature.

Reviews are helpful when you're short on time.


Types of Reviews Databases
Literature reviews and
Systematic reviews

Filter your search results for reviews or systematic reviews
Summaries UpToDate Find clinical recommendations and research summaries


  Databases for clinical support

Use the following databases to find research on clinical practice and care.

Caution: Search results in these databases may exclude non-clinical literature.


Type Databases
Clinical search engines PubMed Clinical Queries Filter results for therapy, diagnosis, etiology, prognosis, and clinical prediction guides
TRIP Search evidence-based information for clinical practice and care


►  Run the search

Enter your search statement into the database search box.


Example search
(heart attack OR myocardial infarction OR heart infarction OR AMI OR MI) AND (aspirin OR acetylsalicylic acid OR ASA)

View this search in a database:

Google Scholar


To get a comprehensive search, use multiple databases.


Step 6: Make search refinements


►  Evaluate the search results for gaps


Search gaps
Relevance Do the publications address your research question?
Coverage Do the results cover your research topics? Are there topics missing?
Level Are the publications too specialized? or too general?
Size Is the quantity of results lower than expected? or higher?
Error Are there notifications of database errors?


►  Change the scope of the search


When this happens: Try to:
I have many results that do not relate to my topic Focus the search
I have few results Expand the search
  Ways to focus the search


Use a more specific topic Instead of: mental illness
Search for: depression

Instead of: back pain
Search for: low back pain


Place “double quotes” around phrases Instead of: quality of life
Search for: “quality of life”

Double quotes let you define precisely how the words will appear.

Without them, results may have the terms in a different order.


Apply filters Use the sidebar filters to sift through results by features, including publication date, article type, study design, and more.

PubMed search filters appear in the left sidebar

PubMed filters in the sidebar


Use controlled vocabulary to enhance the search

Controlled vocabulary is the standardized terms that describe and organize medical topics in a database. 

Databases mark publications with controlled vocabulary to summarize the subject matter.


How to use controlled vocabulary in a PubMed search:

PubMed's controlled vocabulary is MeSH, short for Medical Subject Headings.

– When you find a relevant publication, look for the "MeSH terms" section in the PubMed record.

– Make a note of the MeSH terms of interest and add them to your search statement.

More information: Controlled vocabulary searches in PubMed →


Add an extra topic Instead of: mental health AND exercise
Search for: mental health AND exercise AND mood


Try more ways to focus the search → 

  Ways to expand the search


Add similar terms Instead of: hypertension
Search for: hypertension OR high blood pressure

Instead of: quality of life
Search for: quality of life OR patient satisfaction OR resilience


Use a broader topic Instead of: aortopulmonary septal defect
Search for: congenital heart defects


Examine similar articles Databases often suggest comparable publications for an article.

In PubMed, look to the "Similar articles" section beneath the item's abstract.


Eliminate a topic Instead of: heart attack AND aspirin AND high blood pressure
Search for: heart attack AND aspirin


Try more ways to expand the search → 



A literature search is an iterative process. You will:

–  Run a preliminary search
–  Evaluate the search results
–  Revise the search strategy to address any gaps
–  And repeat the process