Efficacy or effectiveness


What is the difference? Dr Shock forgot. He received a review of a manuscript. Fortunately it will be accepted if…… And one of the mistakes Dr Shock made was confusing the two, using them both for efficacy. After a search on the web Dr Shock will remember the difference, once and for all. He found a clear explanation on medicinescomplete.com. Mind you English is not his native tongue.

Efficacy is: Whether or not an intervention can work under ideal conditions relates to efficacy.1 If the conditions of a trial are optimised, the measurement of the outcome variable may detect even relatively small effects of the treatment. In such a trial, bias is excluded as far as possible, for example by including only patients who are likely to cooperate fully with the medical advice.2 In such a trial, patients should not be treated with concomitant medication and other co-interventions should be avoided. A treatment is efficacious when it proves to be superior to (usually) placebo or another treatment of known efficacy.

Effectiveness is: The pragmatic question of whether an intervention works in routine clinical care relates to effectiveness.1 In this setting, the inclusion criteria for patients are more relaxed. In such a trial, the question is whether the treatment does more good than harm among those to whom it is offered and patients are allowed to accept or reject the treatment, much as would be the case in real-life situations.