Clinical questions may be categorized as either background or foreground. Why is this important?
Determining the type of question will help you to select the best resource to consult for your answer.
Background questions ask for general knowledge about an illness, disease, condition, process or thing. These types of questions typically ask who, what, where, when, how & why about things like a disorder, test, or treatment, etc.
Foreground questions ask for specific knowledge to inform clinical decisions. These questions typically concern a specific patient or particular population. Foreground questions tend to be more specific and complex compared to background questions. Quite often, foreground questions investigate comparisons, such as two drugs, two treatments, two diagnostic tests, etc. Foreground questions may be further categorized into one of 4 major types: treatment/therapy, diagnosis, prognosis, or etiology/harm.
The PICO model is a helpful tool that assists you in organizing and focusing your foreground question into a searchable query. Dividing into the PICO elements helps identify search terms/concepts to use in your search of the literature.
P = Patient, Problem, Population (How would you describe a group of patients similar to you? What are the most important characteristics of the patient?)
I = Intervention, Prognostic Factor, Exposure (What main intervention are you considering? What do you want to do with this patient?)
C = Comparison (What are you hoping to compare with the intervention: another treatment, drug, placebo, a different diagnostic test, etc.? It's important to include this element and to be as specific as possible.)
O = Outcome (What are you trying to accomplish, measure, improve or affect? Outcomes may be disease-oriented or patient-oriented.)
Two additional important elements of the well-built clinical question to consider are the type of foreground question and the type of study. This information can be helpful in focusing the question and determining the most appropriate type of evidence.
Foreground questions can be further divided into questions that relate to therapy, diagnosis, prognosis, etiology/harm
Definitions of Study Types
(From BMJ’s Clinical Evidence Glossary)
Meta-analysis: A statistical technique that summarizes the results of several studies in a single weighted estimate, in which more weight is given to results of studies with more events and sometimes to studies of higher quality.
Systematic Review: a review in which specified and appropriate methods have been used to identify, appraise, and summarize studies addressing a defined question. (It can, but need not, involve meta-analysis). In Clinical Evidence, the term systematic review refers to a systematic review of RCTs unless specified otherwise.
Randomized Controlled Trial: a trial in which participants are randomly assigned to two or more groups: at least one (the experimental group) receiving an intervention that is being tested and another (the comparison or control group) receiving an alternative treatment or placebo. This design allows assessment of the relative effects of interventions.
Controlled Clinical Trial: a trial in which participants are assigned to two or more different treatment groups. In Clinical Evidence, we use the term to refer to controlled trials in which treatment is assigned by a method other than random allocation. When the method of allocation is by random selection, the study is referred to as a randomized controlled trial (RCT). Non-randomized controlled trials are more likely to suffer from bias than RCTs.
Cohort Study: a non-experimental study design that follows a group of people (a cohort), and then looks at how events differ among people within the group. A study that examines a cohort, which differs in respect to exposure to some suspected risk factor (e.g. smoking), is useful for trying to ascertain whether exposure is likely to cause specified events (e.g. lung cancer). Prospective cohort studies (which track participants forward in time) are more reliable than retrospective cohort studies.
Case control study: a study design that examines a group of people who have experienced an event (usually an adverse event) and a group of people who have not experienced the same event, and looks at how exposure to suspect (usually noxious) agents differed between the two groups. This type of study design is most useful for trying to ascertain the cause of rare events, such as rare cancers.
Case Series: analysis of series of people with the disease (there is no comparison group in case series).
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Another way of conceptualizing an evidence hierarcy:
Melncky, B.M. & Fineout-Overholt, E. (2010). Evidence-based practice in nursing & healthcare: A guide to best practice (2nd ed). Philadelphia, PA: Wolters Kluwer/Lippincott Williams & Wilkins.