Full Text
The Full Text of this article is available as a PDF (842.4 KB).
. 1997 Oct 25;315(7115):1090–1096. doi: 10.1136/bmj.315.7115.1090
Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.