1. Center for Advanced Medicine and Clinical Research; Nagoya University Graduate School of Medicine; Nagoya 466-8550 Japan
2. Department of Public Health Sciences; University of Virginia; Charlottesville 22904 Virginia U.S.A.
3. Biostatistics Group, Office of New Drug V; Pharmaceuticals and Medical Devices Agency; Tokyo 100-0013 Japan
4. Department of Biostatistics; Nagoya University Graduate School of Medicine; Nagoya 466-8550 Japan