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Department of Neurology Neurosciences Centre, and Clinical Epidemiology Unit, All India Institute of Medical Sciences, New Delhi Delhi, India
Abstract
It is important to articulate your need for information into a well-formulated clinical question. The question serves as a starting point for literature search and hence must have a degree of focus that strikes a balance between getting too many ‘irrelevant’ articles and ‘not getting any article at all’. Experts often distinguish between ‘focused’ questions and ‘general’ questions. Focused questions specify the type of patients, intervention under consideration, comparison and outcome. General questions usually start with ‘what’, ‘where’ and ‘how’. For example, what is ‘SARS’? What is the pathology of acute myocardial infarction? How do bacteria enter brain? Where does malaria occur? Some authors like the term ‘background’ questions for general questions (and hence foreground for focused questions). These terms mysticise, and hence, I do not favour them.
It is important to articulate your need for information into a well-formulated clinical question. The question serves as a starting point for literature search and hence must have a degree of focus that strikes a balance between getting too many ‘irrelevant’ articles and ‘not getting any article at all’. Experts often distinguish between ‘focused’ questions and ‘general’ questions. Focused questions specify the type of patients, intervention under consideration, comparison and outcome. General questions usually start with ‘what’, ‘where’ and ‘how’. For example, what is ‘SARS’? What is the pathology of acute myocardial infarction? How do bacteria enter brain? Where does malaria occur? Some authors like the term ‘background’ questions for general questions (and hence foreground for focused questions). These terms mysticise, and hence, I do not favour them.
Components of a Focused Clinical Question
The components of a clinical question are often described using the acronym ‘PICO’, where
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P = Patients or population or problem
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I = Intervention
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C = Comparison
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O = Outcome
Let us elaborate them.
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P: ‘P’ may refer to type of patients. You may specify age, sex, race, disease severity and co-morbidity, which should be similar to the patients under consideration or to the type of patients of interest to you. Sometimes, a question arises: Does P stand for patients, population or problem? My answer is all of them. A complete description is ‘population of patients with a problem’. Problem refers to the disease condition. The word ‘population’ comes here because EBM is based on evidence from research. Research typically studies a sample of patients but always attempts to infer about the population of patients represented in the sample. Sometimes, you may only refer to the problem. For example, in the question, ‘In rheumatoid arthritis, is methotrexate more effective in inducing long-term remission than chloroquine?’, only problem (condition or disease) is mentioned.
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I: ‘I’ stands for ‘intervention’ of interest – usually the new intervention. This applies to a treatment question. In case of diagnostic test question, ‘I’ stands for ‘index test’. This means the test which is of interest to you. The most versatile expanded term for ‘I’ is ‘independent’ or ‘input’ variable. In treatment question, the input variable is the ‘intervention’. In diagnostic test question, it is the ‘index test’; in prognosis question, it is the prognostic variable; and in harm question, it is the exposure to potentially harmful agent. Thus, ‘independent’ or ‘input’ variable covers all of these. Some experts expand ‘I’ to ‘indicator’. An indicator variable may indicate the likely prognosis or diagnosis and thus covers a prognostic variable or index test.
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C: ‘C’ stands for ‘comparator’ or ‘comparison’ or ‘control’. I prefer the term ‘comparator’ because ‘comparison’ to some readers means both the interventions and tests – one versus another. Actually only one intervention to which the new intervention is compared comes under this letter.In case of diagnostic test, the comparator is always a ‘gold standard’, which correctly labels (classifies) ‘disease present’ or ‘disease absent’ with perfect accuracy.
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O: ‘O’ stands for ‘outcome’. The word ‘outcome’ here refers to health consequences of exposure or intervention. In case of intervention, it refers to ‘patient relevant outcomes’ like what happens to the patients as a result of treatment. Clinicians usually mean ‘mortality and morbidity’, but outcome also includes adverse effects related to the intervention. You should also consider both beneficial as well as adverse effects of the intervention. Outcome in case of diagnostic test is accurate diagnosis of the patient’s problem or condition.
Variations of PICO
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PECO: Here ‘E’ stands for ‘exposure’. In questions about harm, the potentially harmful agent to which the patients or people are exposed will come under ‘exposure’. In prognosis question, the prognostic factor may be taken as the ‘exposure, even though it may be a demographic characteristic of the patients like age. Questions like ‘whether mobile phone use causes brain tumour’ is better formulated with ‘E’ in PECO than ‘I’ in PICO.
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PIO or PEO: Sometimes, there is no separate ‘çomparator’. For example, if all patients are exposed, there is no comparison with unexposed, though comparison may occur across different levels of exposure. If our question is whether age is a prognostic factor for outcome after head injury, we are comparing those with older age to those with younger age, or vice versa, but all patients have some ‘age’. If you do not know which age to compare to which one, it is not possible to separately identify E and C. Often there is a linear relationship with perceptible change in outcome for every 5-year change in age.
If you are interested in the question of whether blood pressure (BP) is related to vascular events, you may not be able to state which blood pressure to compare to which one? In fact, you may think (and rightly so) that both lower as well as higher BP may be related to increase in vascular events. In such a situation, it is much easier to use the version ‘PEO’ than ‘PECO’.
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