An official website of the United States government
The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before
sharing sensitive information, make sure you’re on a federal
government site.
The site is secure.
The https:// ensures that you are connecting to the
official website and that any information you provide is encrypted
and transmitted securely.
Alam SJ, Romero-Severson E, Kim JH, Emond G, Koopman JS.Alam SJ, et al. Among authors: koopman js.Epidemiology. 2010 Sep;21(5):669-75. doi: 10.1097/EDE.0b013e3181e9e901.Epidemiology. 2010.PMID: 20585251Free PMC article.