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.
Note: the overall time scale is 192 years, or 10,000 weeks. One data point is represented for every 10 weeks (hence 1000 data points are represented here). The red arrows relate to specific zones of the graph that are discussed in the text.
