The ethics of single-system (n=1) research

Abstract

This paper explores the relationship between the methodological and ethical features of the single-system (n = 1) design. Four issues are addressed, the first of which is the claim that the design is deficient in external validity and thereby lacks ethical justification in respect of experimental risk. It is argued against this that the single-system design is more generalisable than is generally supposed, and that its structure does much to minimise such risk. Second, the use of a control group in group studies is often seen to present ethical drawbacks, especially with regard to randomisation and the withholding of treatment, and the absence of a control group in single-system studies is often commended on these grounds. However, although there is no randomisation, the single-system design commonly involves some form of treatment denial, and gives rise to comparable ethical criticism. Third, although single-system designs avoid some of the difficulties of group studies in relation to informed consent, they give rise to other ethical problems in this respect. Finally, single-system studies are rightly praised for their compatibility with everyday clinical practice, but this characteristic can tend to blur the distinction between the therapist-as-clinician and the therapist-as-researcher, with problematic ethical consequences. In conclusion, it is argued that, as the single-system study grows in acceptability and popularity, physiotherapists should scrutinise more closely its ethical strengths and weaknesses.