Full text
PDF
. 1968 Mar;58(3):517–527. doi: 10.2105/ajph.58.3.517
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.