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.
Within each site, values followed by the same letter are not significantly different at the 0.05 level of probability. Vertical bar indicate standard deviation (days).
