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.
Sun Y, Strandberg-Larsen K, Vestergaard M, Christensen J, Nybo Andersen AM, Grønbaek M, Olsen J.Sun Y, et al.Am J Epidemiol. 2009 Feb 1;169(3):313-22. doi: 10.1093/aje/kwn334. Epub 2008 Dec 8.Am J Epidemiol. 2009.PMID: 19064645