Full Text
The Full Text of this article is available as a PDF (423.3 KB).
. 1997 Feb 15;314(7079):492–496. doi: 10.1136/bmj.314.7079.492
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.