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.
The conventions are the same as in Fig. 2. The regression lines shown in the figure were determined by linear regression analysis performed without weighting of the data.
