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.
Maclure M, Greenland S.Maclure M, et al. Among authors: greenland s.Am J Epidemiol. 1992 Jan 1;135(1):96-104. doi: 10.1093/oxfordjournals.aje.a116206.Am J Epidemiol. 1992.PMID: 1736665