Bibliographical noteFunding Information:
• R. Dennis Cook and Douglas M. Hawkins are both Professors in the Department of Applied Statistics, University of Minnesota, SI. Paul, MN 55108. The work of Cook was supported in part by National Science Foundation Grant DMS-8801544, and that of Hawkins was supported in part by National Science Foundation Grant DMS-8902571.
• David Ruppert is Professor, School of Operations Research and Industrial Engineering, Cornell University, Ithaca, NY 14853. Douglas G. Simpson is Associate Professor, Department of Statistics, University of Illinois, Champaign, IL 61820. Ruppert was supported by National Science Foundation Grant DMS-880029and by the U.S. Army Research Office through the Mathematical Sciences Institute at Cornell. Simpson was supported by a National Science Foundation Postdoctoral Research Fellowship.