1 Department of Clinical Epidemiology, Leiden University Medical Center, Leiden, the Netherlands, b.b.l.penning_de_vries@lumc.nl.
2 Departments of Clinical Epidemiology and Biomedical Data Sciences, Leiden University Medical Center, Leiden, the Netherlands.
3 Department of Statistics, University of Washington, Seattle, Washington, Vaccine and Infectious Disease Division, Fred Hutchinson Cancer Research Center, Seattle, Washington.