Appraising directness

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Before even reading an article, the first thing we must do is evaluate directness, i.e. how well the PEO in the study (the research question), corresponds with our own PEO (the clinical question). The problem of directness is very common. Directness issues arise because investigators are constrained by their budgets to answer very narrow, focused questions. In contrast, healthcare professionals in the real world are interested in a very broad range of issues. These differences are summarized in Table 2.1.

Because the evidence doesn't always provide a direct answer to our clinical question, we are often constrained to use available information. For example, we have used studies in men to manage coronary disease in women for many decades[1]. Also, few beta-blockers have been proven to reduce the risk of stroke in hypertensive patients and yet specialty societies agree that any beta-blocker may be used[2].

There are instances however, when we should be very cautious in using indirect evidence. For example, a study on the anti-arrhythmic drug flecainide for acute myocardial infarction (MI)[3] showed that, despite the beneficial effect on cardiac rhythm (the surrogate outcome), the drug eventually caused thousands of

Table 2.1 The problem of directness: differences in the types of questions asked by researchers and clinicians according to the population of interest (P), the exposures or treatments evaluated (E) and the outcomes monitored (O)

Research Questions

Clinical Questions

P

Because sample size is limited, researchers need to restrict their studies to a few, broadly defined subgroups of patients e.g. the effect of treatment in the young and old.

Clinically, we are often interested in treatment effects in many different subgroups e.g. the effect of treatment in young and old, males and females, sick and healthy, smokers and non-smokers, rich and poor.

E

Researchers usually evaluate a specific exposure e.g. drug preparation, surgical technique or educational strategy.

Clinically, we are usually interested in variations of the exposure e.g. a similar drug belonging to the same class, a similar surgery using a modified technique, or a similar educational strategy using a different educational tool.

Researchers sometimes make inappropriate comparisons e.g. a high dose of one drug versus a low dose of another.

Clinically, we are only interested in fair comparisons.

O

Researchers usually monitor a selected few, easily measurable outcomes e.g. surrogate outcomes such as serum cholesterol and blood pressure.

Clinically, we are more interested in important effects that are sometimes difficult and expensive to measure e.g. clinical outcomes such as pain relief, disability, overall quality of life or mortality.

Researchers at times monitor composite outcomes e.g. instead of measuring the incidence of death alone, they monitor the combined incidence of death, stroke or heart attack. This increases the number of events in a study, and thus decreases the required sample size.

Clinically, we are interested in the effect of treatment on separate outcomes because in composite outcomes 1) the individual components may not be of equal importance to us or 2) the effect of treatment may not be of the same magnitude for each component.

deaths in the setting of an acute MI (the clinical outcome)'4'. If we are to avoid harming patients the way this drug did, we must think twice before assuming that a surrogate outcome, such as reducing cardiac rhythm problems, provides a direct answer to a clinically important question, such as prolonging life.

Evaluating directness is as much an art as it is a science. If you feel the article might provide a reasonably close answer to the question you are asking, then proceed to evaluate it in greater detail. Otherwise, it would be wise to spend your time looking for a closer match.

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