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.
Distribution of propensity scores among users (A) and nonusers (B) of hormonal birth control aged 25–34 years in a nationally representative sample of sexually active nonpregnant US women, National Longitudinal Study of Adolescent Health, 2007–2008.
