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.
Error bars represent the 95% confidence interval. Numbers above the error bars indicate the total numbers considered. Information on frequency of blood donation was not available for 5 individuals.
