1. Department of Epidemiology; College of Public Health, University of Iowa; Iowa City Iowa
2. Hardin Library for the Health Sciences; University of Iowa; Iowa City Iowa
3. Office of Biostatistics and Epidemiology, Center for Biologics Evaluation & Research, U.S. Food and Drug Administration; Silver Spring Maryland
4. Division of Research; Kaiser Permanente Northern California; Oakland California
5. Department of Biostatistics; College of Public Health, University of Iowa; Iowa City Iowa