Full Text
The Full Text of this article is available as a PDF (1.6 MB).
. 1997 Jun;6(Suppl 2):S25–S30. doi: 10.1136/tc.6.suppl_2.s25
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.