Efficacy and effectiveness trials

Abstract

W hat is the difference between efficacy and effectiveness studies? In designing a clinical trial, we can go one of two ways. The first is to see whether the intervention has any promise of being as good as or better than existing treatments. This is the realm of efficacy trials—that is, can the treatment work under ideal circumstances? On the other hand, there are treatments that can work, but for a variety of reasons, they don’t: adverse reactions, demanding treatment schedules, the patient saying, “Thanks Doc, but no thanks.” This is the realm of effectiveness studies: does the intervention work under real-life conditions?1 The distinction between the types of studies is important for readers of the studies, because it dictates the degree to which the findings can be applied to clinical practice in the near future. Efficacy trials alert the reader to promising new treatments. But as we’ll see, they may not have been delivered under realistic conditions and may have included patients who are not typical of those seen routinely. So, the efficacy trials may be less useful in the real world. Effectiveness studies are closer to who is seen and what is done clinically but may not show the real potential of the treatment. But, as is typical, if there’s a term for something that everybody understands, someone has to come along and make up a new one, just for the sake of confusion. So, effectiveness trials have also been called pragmatic or management studies, and efficacy trials are also known as explanatory studies.2 We can live with the synonyms for effectiveness trials, because they do describe what the studies are about—they are more “real life” than efficacy trials and often involve management of the condition. As far as being explanatory, though, we’d say close but no cigar. The goal of such a trial is rarely to explain anything but simply to see whether an intervention works. So we’ll stick to our original terms. We will continue to use the example from our article on randomized clinical trials that appeared in the February 2009 issue of Community Oncology. In that column, we discussed whether platinum and diamonds (PAD) is better than treatment as usual (TAU) in alleviating the symptoms of malignant hypertrophy of the ego (MHE), a terminal disorder that afflicts politicians of all stripes (and has been known to affect the occasional clinician). Let’s design a study and see how the choice of effectiveness versus efficacy influences our decisions at each stage.