1. Epidemiology Branch, Division of Intramural Population Health Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland
2. Department of Obstetrics and Gynecology, University of Utah Health Sciences Center, School of Medicine, Salt Lake City
3. Epidemiology Branch, Division of Intramural Population Health Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland3Center for Financing, Access, and Cost Trends, Agency for Healthcare Research and Quality, Rockville, Maryland
4. Department of Statistics, University of Haifa, Haifa, Israel