Dept Biometry & Epidemiology, Medical Univ South Carolina, 135 Cannon street, Suite 303, PO Box 250835, Charleston, SC 29425, USA. almeidaj@musc.edu|Dept Biometry & Epidemiology, Medical Univ South Carolina, 135 Cannon street, Suite 303, PO Box 250835, Charleston, SC 29425, USA. almeidaj@musc.edu