Accepted for Publication: December 22, 2011.
Author Contributions:Study concept and design: Duranceau and Liberman. Acquisition of data: Martin and Liberman. Analysis and interpretation of data: Liberman and Ferraro. Drafting of the manuscript: Duranceau, Martin, and Ferraro. Critical revision of the manuscript for important intellectual content: Duranceau, Martin, and Liberman. Administrative, technical, and material support: Martin, Liberman, and Ferraro.
Financial Disclosure: None reported.
Previous Presentation: Presented as The Joyce and John Benfield Annual Lecture at the University of Chicago; October 20, 2011; Chicago, Illinois.