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 shaded area indicates for each iteration the data between the 40th and the 60th percentile and between the 25th and 75th percentile.
