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.
Circles represent times of entry; solid circles are known times of birth and open circles are entries after birth. Squares are departure times where solid squares are known times of death and open squares are out-migration. Solid triangles indicate individuals known to be alive until the end of the study and vertical bars indicate unknown type of departure.
