Department of Epidemiology and Biostatistics, University of South Carolina, Columbia, SC, USA.|Department of Epidemiology and Biostatistics, University of South Carolina, Columbia, SC, USA.|Department of Mathematics, University of Arizona, Tucson, AZ, USA.|Department of Mathematics, University of Arizona, Tucson, AZ, USA.|Department of Quantitative Sciences, Baylor College of Medicine, Houston, TX, USA.|Department of Environmental Health Science, University of South Carolina, Columbia, SC, USA.|Department of Quantitative Sciences, Baylor College of Medicine, Houston, TX, USA.|Department of Biostatistics, Yale School of Public Health, New Haven, CT, USA.