Types of outcomes
One simple way of initially filtering information is by looking at the outcomes that were measured in the study. These can be broadly split into two types:
- patient oriented outcomes (POEMs)
- disease oriented outcomes (DOEs), also called surrogate outcomes.
As the name suggests, a POEM is an outcome that matters to a patient. The study has used an outcome which is a direct measure of:
- How a patient feels, for example an improvement in quality of life following counselling for depression.
- How a patient functions, for example an improvement in walking distance following knee surgery.
- How a patient survives such as a reduction in death from heart attacks with lipid lowering drugs.
The outcome is clinically meaningful. It matters to the patient and of course, therefore, to the health care professional.
Surrogate outcomes (DOEs)
A surrogate outcome is a laboratory measurement or a physical sign used as a substitute for a clinically meaningful outcome.
Some examples of surrogate outcomes include:
- Reduction in cholesterol levels with lipid lowering drugs
- Improvement in XRay appearance following knee surgery
- Reduction in anti-depressant use following counseling for depression
The effect of an intervention on a surrogate outcome should predict the effect on the desired clinical outcome. However, the surrogate outcome may be of little interest to the patient. What they want to know is “will I feel better” or “will I live longer”?
Disadvantages of surrogate endpoints
Therapeutic interventions have multiple effects that often are not reflected by a single surrogate outcome.
In particular, the surrogate outcome may not measure drug safety. For example, patients given Flecainide following a heart attack were found to have their ventricular ectopics suppressed. However, this did not lead to the expected reduction in mortality. In fact, there was an increase in cardiac arrests.
There are many examples in medicine where over-reliance on surrogate outcomes has been misleading and sometimes harmful.
|A searchable database of POEMs. Subscription needed.||Includes daily emailed POEM. Many journals such as the BMJ include a weekly POEM.|