Cochrane Library Tutorial
Previous Previous Next Next

'P I C O' examples


INTERVENTIONS cover a wide range of activities from drug treatments and other clinical therapies, to lifestyle changes (e.g. diet or exercise) and social activities (e.g. an education program). Interventions can include individual patient care or population health activities (e.g. screening for diseases such as cervical or prostate cancer).


A 28-year-old male presents with recurrent furunculosis (skin boils) for past 8 months; these episodes have been treated with drainage and several courses of antibiotics but keep recurring. He asks if recurrences can be prevented. To convert this to an answerable question, use the P I C O method as follows :


‘In patients with recurrent furunculosis, do prophylactic antibiotics, compared to no treatment, reduce the recurrence rate?’

 P   Population/patient  =   patients with recurrent furunculosis
 I   Intervention/indicator  =   prophylactic antibiotics
 C   Comparator/control  =   no treatment
 O   Outcome  =   reduction in recurrence rate of furunculosis

Aetiology and risk factors

AETIOLOGY and RISK FACTORS relate to questions that probe possible causes of a disease or illness. They are the reverse of intervention questions because they deal with the harmful outcomes of an activity or exposure. Such questions commonly arise in relation to public health issues, such as whether eating certain foods increases the risk of heart disease, or being exposed to an environmental chemical increases the risk of cancer, and so on.


George wants to discuss the possibility of a vasectomy. He says he has heard something about vasectomy causing an increase in testicular cancer later in life. You know that the risk of this is low but want to give him a more precise answer.


‘In men, does having a vasectomy (compared to not having one) increase the risk of getting testicular cancer in the future?’

 P   Population/patient  =   adult males
 I   Intervention/indicator  =   vasectomy
 C   Comparator/control  =   no vasectomy
 O   Outcome  =   testicular cancer

Frequency or rate

Questions of FREQUENCY (prevalenceGlossary link image) are about how many people in the population have a disease or health problem, such as what is the frequency of hearing problems in infants or the prevalence of Alzheimer’s disease in the over 70s. If the question also includes a time period, such as for cases of influenza in winter versus summer, it becomes a question of rate (incidence).


Mabel is a 6-week-old baby at her routine follow-up. She was born prematurely at 35 weeks. You want to tell the parents about her chances of developing hearing problems.


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

 P   Population/patient  =   infants
 I   Intervention/indicator  =   premature
 C   Comparator/control  =   full-term
 O   Outcome  =   sensorial deafness


Diagnosis questions are concerned with how accurate a diagnostic test is in various patient groups, and in comparison to other available tests. Measures of test accuracy include its sensitivity and specificity.


Julie is pregnant for the second time. She had her first baby when she was 33 and had amniocentesis to find out if the baby had Down's Syndrome. The test was negative but it was not a good experience as she did not get the result until she was 18 weeks pregnant. She is now 35, one month pregnant and asks if she can have a test that would give her an earlier result. The local hospital offers serum biochemistry plus nuchal translucency ultrasound as a first trimester test for Down's Syndrome. You wonder if this is as reliable as conventional amniocentesis.


‘For pregnant women, is nuchal translucency ultrasound plus serum biochemistry testing in the first trimester as accurate (ie with equal or better sensitivity and specificity) as conventional amniocentesis for diagnosing Down's Syndrome?’

 P   Population/patient  =   pregnant women
 I   Intervention/indicator  =   nuchal translucency ultrasound plus serum biochemistry (first trimester)
 C   Comparator/control  =   conventional amniocentesis
 O   Outcome  =   accurate diagnosis (measured by sensitivity and specificity) of Down's Syndrome (trisomy 21)


Questions about phenomena can relate to any aspect of clinical practice, such as physical examination, taking a health history or barriers to successful participation in health care. Such questions usually involve a population (P) and an outcome (O) but not an intervention or comparator.


Mary is a mother who is concerned about her 3-year-old. He has a fever. After you have examined him you conclude that he has a viral infection. Mary asks ‘But what if he has a fever again during the night?’ You want to understand her concerns so that you can reassure her.


For mothers of children with a fever, what are the principal concerns?

 P   Population/patient  =   mothers of children with fever
 O   Outcome  =   principle concerns


Try the following exercises; the first is an example of a Phenomenon.

Exercise: 1

When giving immunisation injections to children, you notice that many of the children make distinctive facial expressions when they receive the injection and you wonder how these expressions are related to their experience of pain.

 P   Population/patient  =       
 O   Outcome  =       

Exercise: 2

"Is there evidence to suggest that the prophylactic use of vitamin B12 supplements is effective in improving the quality of life (specifically cognition) of apparently healthy older people?"

Exercise: 3

"Would you recommend self-monitoring of blood glucose levels for patients with Non-Insulin Dependent Diabetes Mellitus (NIDDM)?"

Exercise: 4

"In elderly patients with congestive heart failure, is digoxin effective in reducing the need for rehospitalization?"

Exercise: 5

"Is glucosamine sulphate an effective agent in the short-term treatment of osteoarthritis?"

Exercise: 6

"In a 70 year old woman with primary insomnia and a previous adverse reaction to hypnotics, can cognitive behavior therapy improve sleep quality and duration?"


Previous Previous Next Next