Abstract

Clinical trials and other forms of evaluation of medical treatment are held to give an objective assessment of the ‘clinical effectiveness’ of the medical treatments under evaluation. This kind of evaluation is central to the evidence-based medicine movement, as it provides a basis for the rational selection of treatment. The ethical status of randomised clinical trials is widely agreed to depend crucially upon the state of equipoise regarding which of two (or more) treatments is more (or most) effective in a defined population. However, the meaning and nature of ‘clinical effectiveness’ are unclear. in this paper, I discuss the proposals to define clinical effectiveness as a relational property and as an intrinsic property, and the way effectiveness may supervene upon more fundamental physical properties of treatments. I discuss whether effectiveness is a single property or a family of properties; the types of outcome which can be explained by effectiveness properties; and the relationship between ‘objective’ and ‘preference’ outcomes. This paper suggests that while it may be possible to put clinical effectiveness on a proper metaphysical footing, in practice the language of clinical effectiveness is more properly a topic of the human sciences than of the natural sciences.