1. Department of Medical Biology, Faculty of Medicine, Cukurova University, 01330, Balcali. Adana. Turkey
2. Department of Epidemiology and Public Health, Yale University School of Medicine, 60 College Street, New Haven, CT 06520–8034
3. Current address and reprint requests: Departments of Biology and Epidemiology, the University of Michigan, 109 Observatory Street, Ann Arbor, MI 48109–2029.