Correspondence: Dr Rivara, Department of Pediatrics, Child Health Institute, University of Washington, 6200 74th St NE, Ste 120B, Seattle, WA 98115 (fpr@u.washington.edu).
Author Contributions: Study concept and design: Christakis, Joffe, Keren, Davis, Shah, and Rivara. Acquisition of data: Christakis. Drafting of the manuscript: Keren and Rivara. Critical revision of the manuscript for important intellectual content: Christakis, Joffe, Keren, Davis, and Shah.
Financial Disclosure: None reported.