1. a Department of Statistics , George Mason University , Fairfax , VA , 22030 , USA
2. b Department of Epidemiology and Public Health , University of Maryland Greenebaum Cancer Center , Baltimore , MD , 21201 , USA
3. c Department of Biostatistics , University of Washington , Seattle , WA , 98195 , USA
4. d HSR&D Center of Excellence , 1100 Olive Way, Seattle , WA , 98101 , USA