- Correspondence to Dr Lauren M Rossen, Office of Analysis and Epidemiology, National Center for Health Statistics, Centers for Disease Control and Prevention, 3311 Toledo Rd, Room 6114, Hyattsville, MD 20782, USA;
- Received December 5, 2012
- Revised June 24, 2013
- Accepted September 2, 2013
- First published September 26, 2013.
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