Correspondence
Statistics in question
Br Med J (Clin Res Ed) 1981; 283 doi: https://doi.org/10.1136/bmj.283.6303.1401-c (Published 21 November 1981) Cite this as: Br Med J (Clin Res Ed) 1981;283:1401This is a PDF-only article. The first page of the PDF of this article appears above.