1. Division of Biostatistics, Office of Surveillance and Biometrics, Center for Devices and Radiological Health; Food and Drug Administration; Silver Spring, Maryland U.S.A.
2. Division of Biometrics V, Office of Biostatistics, Center for Drug Evaluation and Research; Food and Drug Administration; Silver Spring, Maryland U.S.A.
3. Division of Biometrics IV, Office of Biostatistics, Center for Drug Evaluation and Research; Food and Drug Administration; Silver Spring, Maryland U.S.A.
4. Biostatistics Research Branch, Division of Clinical Research; National Institute of Allergy and Infectious Diseases, National Institutes of Health; Rockville, Maryland U.S.A.