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.
Solid lines denote smoothed values and shaded areas on each plot represent 95% confidence intervals. Dashed line at y = 0 displayed on each plot.
