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.
In infants born prematurely, compared to those born at full term, what is the subsequent lifetime prevalence of sensory deafness?
|P: infants||I: premature||C: full term||O: sensorial deafness|
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.
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:
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).