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.
Boxes indicate the 1st and the 3rd quartiles, the median is shown as a black line, whiskers mark the 9th and 91st percentiles, red triangles represent mean concentrations and blue circles are outliers.
