1. Department of Urology, UMAE Hospital de Especialidades, Centro Médico Nacional Siglo XXI, Instituto Mexicano del Seguro Social, México D.F., México.
2. Department of Health Research, Clinical Research Training Center, Instituto Mexicano del Seguro Social, México D.F., México.
3. Department of Urology, University of California, Irvine, Irvine, California.