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PICO Searching

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

Before You PICO

The first step is to always see if you can find a Meta-Analysis, Systematic Review or Evidence-Based Guideline on your topic. To do this, there are two main places to search:

Because of the nature of these resources, you will not do a full PICO-style search in them. Their search features are much more simplistic, so you would do a standard keyword search to see what comes up in the results. You may not find anything and that is ok. There may be systematic reviews or guidelines from other sources that will appear in your search results when you run a PICO search.

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



Building Your Search String

Now that you have created your synonyms, you need to know a little bit about how databases and search engines work in order to ensure you create a search string that retrieves the types of results you want.

Boolean Logic

  • Most databases and search engines understand at least three of the main logic operators: AND, OR, NOT
    • An operator is a word that is read as something the engine DOES, not as a word to search
    • Operators allow you to combine keywords in different ways
  • AND
    • Requires the results to contain both or all of the terms combined with AND
    • Narrows your results - the more ANDs you use, the fewer results you will retrieve


  • OR
    • Results contain either, both, or any combination of the terms combined with OR 
    • Expands your results - use OR between synonyms


  • NOT
    • Results will not contain ANY articles that used the term(s) indicated after NOT
    • Narrows your results - careful! This deletes any results that may also use a term you want to find




  • If you have 2 or more words that have to appear in a certain order, put them in quotation marks. 
  • "this is a phrase" the quotes tell the search to find the words in that specific order, and not scattered throughout the text
    • "hearing loss" would be an example phrase from our synonyms above


  • Computers read search instructions from left to right and will follow the operators as they appear
  • Parenthesis work the same way as in mathematical equations: they tell the computer to do whatever is inside of them FIRST
  • This is important to know because you generally want the computer to find all the synonyms for one element of your search BEFORE combining the second, third and/or fourth elements together
    • The goal of synonyms is to find as many articles on each individual PICO element as you can, then retrieve the articles that mention all four PICO elements in some way
  • Example: (premature OR premie OR pre-term) AND (infant OR baby OR newborn)

Simple Rules

  • If you need an easy list of steps and rules to remember:
    • Create a keyword/synonym chart for your PICO
    • All synonyms(rows) within a column are combined with OR
    • Between columns, you combine with AND
    • Lists of OR'ed terms should have parenthesis around them

One-Line Search String

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


Multi-Line Search String

Many databases allow you to build a search using multiple lines, as well. If you use the PubMed 'Advanced' search page, 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 PubMed Advanced search, for example: