Full text
PDF
. 1960 Apr;4(2):91–111. doi: 10.1017/s0025727300025205
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.