1. Biostatistics Unit, Clinical and Translational Research Center Keio University Hospital 35 Shinanomachi, Shinjuku‐ku Tokyo 160‐8582 Japan
2. Graduate School of Comprehensive Human Sciences University of Tsukuba 1‐1‐1 Tennodai Tsukuba Ibaraki 305‐8575 Japan
3. Department of Biostatistics, Faculty of Medicine University of Tsukuba 1‐1‐1 Tennodai Tsukuba Ibaraki 305‐8575 Japan