Research Article Controlled trials in single subjects. 2. Limitations of use. BMJ 1991; 303 doi: https://doi.org/10.1136/bmj.303.6795.175 (Published 20 July 1991) Cite this as: BMJ 1991;303:175 Article Related content Metrics Responses Peer review This is a PDF-only article. The first page of the PDF of this article appears below.