1. a Department of Veterans Affairs , War-Related Illness and Injury Study Center , Washington , DC , USA
2. b Department of Preventive Medicine and Biometrics , Uniformed Services University of the Health Sciences , Bethesda , Maryland , USA
3. c MedStar Research Institute , Hyattsville , Maryland , USA
4. d Health Research and Analysis , Rockville , Maryland , USA
5. e EPICON Associates , Silver Spring , Maryland , USA
6. f Analytic Services, Inc. , Arlington , Virginia , USA