Research Article
Publication.
Br Med J (Clin Res Ed) 1983; 286 doi: https://doi.org/10.1136/bmj.286.6374.1341 (Published 23 April 1983) Cite this as: Br Med J (Clin Res Ed) 1983;286:1341This is a PDF-only article. The first page of the PDF of this article appears above.