1. John P. Morgan is Professor, Department of Statistics, Virginia Tech, Blacksburg, VA 24061-0439 . Xiaowei Wang is Senior Statistician, Glaxo Smith Kline, King of Prussia, PA 19406. J. P. Morgan was supported by the United States National Science Foundation grant DMS06-04997, as was Xiaowei Wang while a graduate student at Virginia Tech. J. P. Morgan also extends warm thanks to the Isaac Newton Institute for Mathematical Sciences, wherein a portion of this work was completed.