Skip to Main Content

PICO Searching

Helpful guide to get you started on your clinical question literature searches

Breaking PICO Down

When you create a PICO question, you are actually thinking about how discrete topics relate to each other. Each discrete topic: your P, your I, your C and your O, will probably all have different ways of being expressed when an author writes about them - synonyms. When you use databases or search engines, they only retrieve what you type in, nothing more and nothing related. It is up to you to think of how an author might express your topics in their writing in order to expand the possibility of catching all the relevant articles.

It's helpful to create a chart to stay organized. Place your PICO elements at the top of a column, then write the possible synonyms in the row(s) below.

Clinical Question:
In infants born prematurely, compared to those born at full term, what is the subsequent lifetime prevalence of sensory deafness?

Keyword/Synonyms Chart:

P: infants I: premature C: full term O: sensorial deafness







pre term


full term


39 weeks

40 weeks

sensorial deafness

hearing loss



Boolean Operators

Computers understand mathematical logic, so when you set up a search string, there are three main operations you can do. These operations are represented with three short words, known as Boolean Operators. Each operator tells the computer to perform a different type of action between the terms, or sets of terms, in your search.

  • Tells the database to return results that include both the keywords anywhere in the results.
  • Links different aspects of your research question together to find both concepts in the set of returned results.
  • Narrows your results.
  • Example: birds AND bees

Two circles, one labeled "birds" and the other labeled "bees", intersecting. The area where they intersect is highlighted.

  • Tells the database to return results that include either of the keywords anywhere in the results.
  • Links synonymous terms or concepts - use between words or phrases that represent the same idea.
  • Expands your results.
  • Example: birds OR bees

Two circles, one labeled "birds" and the other labeled "bees", intersecting. The entire area is highlighted.

  • Tells the database to return results that do not include a certain keyword.
  • Rids results of items that that contain a certain element of research topic.
  • Narrows your results.
  • Example: birds NOT bees

Two circles, one labeled "birds" and the other labeled "bees", intersecting. Only the area labeled birds is highlighted.

Search Strings

Search strings allow you to combine terms to search for articles and other resources. You can do this with a single line or many. Click the tabs to learn more.

Using our example from above and the operators and other search rules we've learned, we can create a PICO search string that we can type into a one line search box.


(infant OR infants OR newborn OR baby OR babies) AND (premature OR "pre term" OR pre-term OR premie) AND ("full term" OR full-term OR "39 weeks" OR "40 weeks") AND ("sensorial deafness" OR deaf OR "hearing loss")

Notice the rules we've followed:

  • All synonyms are combined with OR
  • Lists of OR'ed terms are in parenthesis
  • Phrases are placed in quotation marks
  • Each PICO element is combined with AND


A screenshot of a single-string search in PubMed

Many databases allow you to build a search using multiple lines, as well. If you use CINAHL, PsycInfo, and many others, you can:

  • Add search lines that are automatically combined with AND
  • Type all the synonyms combined with OR for your P on the top line
  • Type all the synonyms combined with OR for your I on the next line, and so forth, line by line
  • The database will automatically place parenthesis around the content of each search line for you


In CINAHL Advanced search, for example:

Multi-Line search string query in CINAHL

Database Filters

In PubMed, CINAHL and other clinically-focused databases, on the left-hand side of the results list there will often be a set of filters. These filters help narrow down your question even more - especially PubMed.

In foreground questions we often have a P that is a combination of age, sex, location AND problem. For the sake of building database searches, it is almost always best to use the problem or disease as the P in your synonym chart and initial search. Due to the constraints of ethical research, cost of research, etc. specifics such as race, location of study, age and sex are items you want to save for last. See how much is out there in general before tacking on these qualifiers, because they are sure to severely reduce the number of results you find.

PubMed has filters for all of these qualifiers  (you may need to click "show additional filters"), with multiple options under each filter (click "customize" to see a list of all options).

Filters on a PubMed search