1. Yu-Ching Cheng, Brian L. Rostron, Hannah R. Day, Lynn C. Hull, Alexander Persoskie, Bridget K. Ambrose, and Nicolette Borek are with the Office of Science, Center for Tobacco Products, US Food and Drug Administration, Silver Spring, MD. Cassandra A. Stanton and Kristie Taylor are with Westat Inc, Rockville, MD. Mark J. Travers is with Roswell Park Cancer Institute, Buffalo, NY. Kevin P. Conway is with National Institute on Drug Abuse, Bethesda, MD.