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 dotted line indicates the 50th percentile (the median) and the shaded error indicates the interquartile range (the range between the 25th and 75th percentile). The 25th, 50th and 75th percentile values are provided under each plot.
