School of Clinical Dentistry, The University of Sheffield, Sheffield, South Yorkshire S10 2TN, UNITED KINGDOM.
Evidence based medicine uses hierarchies of evidence to justify knowledge claims that are made. These knowledge claims are important because they dictate which treatment interventions are provided and funded, medicolegal standards and the medical research agenda. It is therefore interesting that different hierarchies can be used as this suggests that knowledge claims can be justified in different ways. This thesis presents a critical analysis of evidence based medicine, using the method of analytical philosophy, to improve understanding of the concept. The thesis is divided into two sections. In the first section a systematic review and thematic analysis of hierarchies of evidence is presented; the arguments used to rank systematic reviews, randomised controlled trials and expert opinion within hierarchies are analysed, and the properties used to rank different study designs are analysed. Five factors, independent of study design, that have influenced the development of hierarchies are then presented and it is argued that a lack of theoretical support for hierarchies has led to their proliferation. In the second section the claims that evidence based medicine is rational, science and a new Kuhnian paradigm are analysed. It is argued that evidence based medicine can be substantively rational but this means that knowledge claims can be both rational and inconsistent dependent upon any value commitments that are held. It is then argued that evidence based medicine cannot be science because it does not use scientific method and it cannot be a new Kuhnian paradigm because it is not science, it was not preceded by a revolutionary crisis and it is not incommensurable with previous versions of medicine. The analysis presented strips evidence based medicine of power and has important implications for the status of knowledge claims that are made.