From the aDepartment of Biostatistics, School of Public Health, University of Michigan, Ann Arbor, MI; bCenter for Statistical Consultation and Research, University of Michigan, Ann Arbor, MI; cDepartment of Biostatistics, Mailman School of Public Health, Columbia University, New York, NY; dDepartment of Environmental Health Sciences, University of Michigan, Ann Arbor, MI; eInstitute for Social Research, University of Michigan, Ann Arbor, MI; fDepartment of Civil and Environmental Engineering, University of Michigan College of Engineering, Ann Arbor, MI; and gVista Analytical Laboratory, El Dorado Hills, CA.
Submitted 1 October 2008; accepted 15 October 2009; posted 8 April 2010.
Supported by The Dow Chemical Company through an unrestricted grant to the University of Michigan.
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Correspondence: Brenda W. Gillespie, Center for Statistical Consultation and Research, 3550 Rackham Building, University of Michigan, Ann Arbor, MI 48109–1070. E-mail: bgillesp@umich.edu.
