Biometric Research Branch, US National Cancer Institute, Bethesda, MD 20892-7434, USA. rsimon@nih.gov|Biometric Research Branch, US National Cancer Institute, Bethesda, MD 20892-7434, USA. rsimon@nih.gov|Biometric Research Branch, US National Cancer Institute, Bethesda, MD 20892-7434, USA. rsimon@nih.gov|Biometric Research Branch, US National Cancer Institute, Bethesda, MD 20892-7434, USA. rsimon@nih.gov