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.
Examples of polynomial models representing change across time. The black line represents no change across time (intercept-only); the blue line represents linear change; the green line represents quadratic change; the red line represents cubic change
