1. a Department of Mathematics and Statistics , University of Maryland , Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland, 21250, U.S.A.
2. b Department of Epidemiology and preventative Medicine , University of Maryland School of Medicine , Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland, 21250, U.S.A.
3. c Department of Statistics , University of Georgia , Athens, Georgia, 30605, U.S.A.