1. Center for Access and Delivery Research and Evaluation, Iowa City Veterans Affairs Health Care System , Iowa City, Iowa , USA
2. Department of Internal Medicine, University of Iowa Carver College of Medicine , Iowa City, Iowa , USA
3. Department of Biostatistics, University of Iowa College of Public Health , Iowa City, Iowa , USA
4. Department of Epidemiology, University of Iowa College of Public Health , Iowa City, Iowa , USA