1. Brent A. Johnson is Assistant Professor, Department of Biostatistics, Emory University, Atlanta, GA 30322 . D. Y. Lin is Dennis Gillings Distinguished Professor and Donglin Zeng is Associate Professor , Department of Biostatistics, University of North Carolina, Chapel Hill, NC 27599. This research was supported by National Institutes of Health grants P30 ES10126, T32 ES007018, and R03 AI068484 (B.J.); R37 GM047845 (D.L.); and R01 CA082659 (D.L. and D.Z.). The authors thank Paul Weiss for preparing the...