1. Department of Mathematical Sciences; University of Texas at Dallas; Richardson Texas 75080 U.S.A.
2. Department of Statistics; University of Michigan; Ann Arbor Michigan 48109 U.S.A.
3. Department of Statistics; University of Connecticut; Storrs Connecticut 06269 U.S.A.
4. Department of Epidemiology and Biostatistics; University of California San Francisco; San Francisco California 94158 U.S.A.