Can it work? Does it work? Is it worth it?

The testing of healthcare interventions is evolving

General practice p 676

The British pioneer clinical epidemiologist Archie Cochrane defined three concepts related to testing healthcare interventions.1 Efficacy is the extent to which an intervention does more good than harm under ideal circumstances (“Can it work?”). Effectiveness assesses whether an intervention does more good than harm when provided under usual circumstances of healthcare practice (“Does it work in practice?”). Efficiency measures the effect of an intervention in relation to the resources it consumes (“Is it worth it?”). Trials of efficacy and effectiveness have also been described as explanatory and management trials, respectively,2 and efficiency trials are more often called cost effectiveness or cost benefit studies.

Almost all clinical trials assess efficacy. Such trials typically select patients who are carefully diagnosed; are at highest risk of adverse outcomes from the disease in question; lack other serious illnesses; and are most likely to follow and respond to the treatment of interest. This treatment will be prescribed by doctors who are most likely to …