Should the single subject design be regarded as a valid alternative to the randomised controlled trial?

In an accompanying article Janine Janosky sets out the case for the use of single subject designs.1 I was asked by my colleague Dr John Mayberry, the editor of the journal, to referee this paper, but felt it would be more appropriate to respond to it, largely to stimulate debate on this issue. I would suggest that the proper applicability of single subject designs is much narrower than this article would imply. I would furthermore warn readers of the dangers of a view that if left to grow unchecked could result in an important undermining of the dominance of the multi-patient randomised clinical trial that is now, with very strong justification, accepted as the cornerstone of evidence based clinical practice—with serious consequences for the choice of appropriate management for future patients. The two key issues are equivocation regarding the ambit of the single subject design, and the robustness of the inference to be drawn from data such as figure 1 in Janosky’s paper.

It is well accepted that clinical expertise is needed to apply the findings of large clinical trials to the individual patient. The doctor’s initial training, ongoing CPD, and clinical experience facilitate the recognition of patients who are not “average” and for whom current evidence based guidelines, which are optimised …