What You Need to Know about PICO

PICO framework for systematic reviews

When doing research on the impact of interventions, systematic reviewers will find that PICO is an indispensable tool. It’s a straightforward method for generating a research topic and determining which studies are qualified to be included in the evaluation of previous work. It takes into account the four fundamental components: 

 The Population (or patients)

 The Intervention

 The Control

 The Outcome

The method in which a review question is structured in this manner brings about a helpful focus and assists review teams in developing specific plans for the work that lies ahead. Consider PICO to be a conceptual glue that binds everything together and serves as a methodological golden thread that goes all the way through your evaluation. 

So how does that actually function in the real world? In order to get a better understanding of how PICO works, let’s take a step-by-step look at the systematic review method.

1. The review question 

The PICO framework serves as the foundation for the majority of the review questions, for instance:

 “In children with nocturnal enuresis (population), how effective are alarms (intervention) versus drug treatments (comparison) for the prevention of bedwetting (outcome)?”

Sometimes the review question does not include the comparison, such as when the review compares the intervention with either no therapy at all or with the care that is typically provided:

 “How effective is physical therapy (intervention) for reducing foot pain (outcome) in runners with plantar fasciitis (population)?”

 “How effective is echinacea (intervention) in preventing common cold (outcome) in healthy adults (population)?”

2. The search strategy 

PICO then contributes to the development of the search strategy by supplying the relevant search phrases that will be utilized to retrieve the studies. Although it is best practice to use PICO to inform the search, it is not typically recommended to include the ‘Outcomes’ aspect of PICO in a search strategy. This is despite the fact that it is excellent practice to use PICO to inform the search. This is due to the fact that it has the ability to lower the memory of the search, which increases the danger of rejecting research that could be possibly relevant (for example, those that measured the outcome of interest but did not report it in the published paper).

Here is a search strategy used for the Cochrane review ‘Wheat flour fortification with iron and other micronutrients for reducing anaemia and improving iron status in populations‘ in Figure 1.

research strategy

Figure 1: Search strategy from the review ‘Wheat flour fortification with iron and other micronutrients for reducing anaemia and improving iron status in populations’

Line 1’s search term “Iron/ or Ferrous Compounds” seeks to find studies that include the intervention of interest (fortified wheat flour). Lines 2–11 expand on this to make the search for studies with a relevant intervention as thorough as feasible. The same search terms are used in this review for both the intervention and the comparator (non-fortified wheat flour).

Line 12 is about the population. The title of this review does not indicate any specific population features. A more focused review would focus on pregnant women or celiac disease patients, for example. In this case, the reviewers are conducting a broad search and simply want to ensure that the studies they find are relevant to humans.

The second section of line 1, “Anemia, Iron-Deficiency/,” could be related to the desired outcomes (iron levels in the study participants will be measured to assess the effectiveness of the intervention). Anemia and iron deficiency, on the other hand, are more likely to be included as baseline features in the study population (i.e. some of the individuals that are randomized to the treatment or the control arm at the start of the trials will have anemia). This is because, as we saw in section 2, identifying outcomes in the search strategy may result in the exclusion of pertinent data.

3. Screening the studies 

After the search has been completed, the inclusion and exclusion criteria that were informed by PICO will enable the effective screening of research. The studies that are imported into Covidence have the convenient ability to be screened alongside a list of inclusion and exclusion criteria at both the title and abstract review stage as well as the full text review stage.

4. Data extraction 

PICO is not merely applied to the process of deciding whether studies are qualified for a review. It is also possible to utilize it to group the study data so that it may be analyzed. The PICO aspects are utilized by the data extraction template that is provided by Covidence in order to organize pertinent information regarding the features of the studies that were included (Figure 2). It is intuitive to use and offers a high level of personalization. Reviewers are better prepared for the analysis and synthesis that will follow if the study data are sorted in this manner.

PICO structure isn’t followed in your review, you can still utilize Covidence to collect and extract data from the studies that are included in the review. The term “population” refers to nothing more than the name that is given to the unit that is arbitrarily assigned to either the intervention or the comparison. Even if that unit is not an individual patient but rather, say, a school, an eye, or a side of the mouth (hello, dentists! ), the data extraction form can still be used to sort the study data according to your preferences. This is because the form was designed to be flexible enough to accommodate a wide variety of different types of units.

5. Data synthesis 

To summarize what we’ve learned thus far, we can say that PICO is utilized to determine the inclusion criteria and to organize study data in preparation for synthesis. Cochrane draws an important line of demarcation between these two applications. The first one is referred to as the review PICO since it is the thing that determines what the review question will be. The second part of this equation is the PICO for each synthesis. This outlines the manner in which the data will be categorized, or potentially divided, into a number of distinct syntheses. These two ideas are separate from a third one, which is the PICO of the studies that were included. This is the PICO that was established by the individual studies whose data were incorporated into the review.

How would something like this actually work? In any case, for the sake of illustration (there have been neither actual trials nor actual systematic reviews), the three PICOs may have the appearance of those depicted in Figure 3. The PICO review generates a question that is relatively open-ended. Reviewers are required to look at the data from eligible studies, each of which has its own PICO, in order to answer it (the PICO of the included studies). After that, the review team applies a PICO to each synthesis in order to make conclusions regarding the appropriate methods for analyzing and presenting the accumulated data.

levels of PICO

Figure 3: The three levels of PICO using the concepts set out in Chapter 3 of The Cochrane Handbook.

The specific manner in which to organize the data to be analyzed in a review will be determined by a number of criteria, including the kind of data and the amount of data involved. You could plan to conduct a subgroup analysis if you have cause to believe that the effect of the therapy might vary according to a characteristic of the population such as age or sex. Examples of such characteristics include gender and age. When designing the protocol or project plan, however, subgroup analyses should be stated and justified in order to avoid the hazards of data dredging and to minimize the danger of bias. 


When it comes to successfully carrying out a systematic review, planning is of the utmost importance. Reviewers are able to better organize each stage of a review with the assistance of PICO, beginning with the formulation of the initial question and continuing through the process of searching for and selecting studies, as well as the data gathering and synthesis stages. A smart way to prepare for the work that lies ahead and to ensure that your analysis remains focused on, and relevant to, the review issue is to take the time to understand PICO and how it may be utilized to best benefit. Taking the time to do so is a good way to prepare for the work that lies ahead.