R.E.G. UPSHUR THE ETHICS OF ALPHA: REFLECTIONS ON STATISTICS, EVIDENCE AND VALUES IN MEDICINE ABSTRACT. As health care embraces the tenets of evidence-based medicine it is impor- tant to ask questions about how evidence is produced and interpreted. This essay explores normative dimensions of evidence production, particularly around issues of setting the tolerable level of uncertainty of results. Four specific aspects are explored: what health care providers know about statistics, why alpha levels have been set at 0.05, the role of randomization in the generation of sufficient grounds of belief, and the role of observational studies. The essay concludes with recommendations to acknowledge the value permeation of outcome measures and suggests that attention to reasoning and argument analysis can augment traditional evidence-based approaches in providing a robust critical approach to medical knowledge. KEY WORDS: evidence-based medicine, medical epistemology, statistical methods In choosing the grounds upon which a general hypothesis should be rejected, personal judgement may and should, properly be exercised. The experimenter will rightly consider all points, on which, in the light of current knowledge, the hypothesis may be imperfectly accurate, and will select tests so far as possible, sensitive to those faults, rather than to others” [1]. ... for in fact no scientific worker has a fixed level of significance at which from year to year, and in all circumstances, he rejects hypothesis; he rather gives his mind to each particular case in light of his evidence and his ideas” [2]. How is evidence produced? The answer according to advocates of Evidence-Based Medicine is through well-designed empirical studies. How do research results become accepted as valid? Usually, for treat- ments, when statistical significance has been achieved at a 5% level. Despite a growing literature on the need for clinical endpoints to determine the relevance of research results, and the creation of clinically relevant indices such as the number needed to treat, the 5% level is adhered to in both estimation and hypothesis testing. It remains the fundamental determination of significance. Why is this important? Evidence is produced, evaluated and published for scientific, clinical and commercial uses. Increasingly, medical knowl- edge is expressed and described in statistical or probabilistic terms. Medical information is of immense interest to the media and the public at large. With the advent of the information age and readily accessible Theoretical Medicine 22: 565–576, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands.