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.
Incidence rate (IR) is calculated per 1000 person-years. Smoking status is described in the Study Design and Study Population subsection of the Methods section.
