1. Philadelphia VA Medical Center; Philadelphia PA USA
2. Center for Clinical Epidemiology and Biostatistics; University of Pennsylvania School of Medicine; Philadelphia PA USA
3. VA Connecticut Healthcare System; West Haven CT USA
4. Yale University School of Medicine; New Haven CT USA
5. VA Greater Los Angeles Healthcare System; Los Angeles CA USA
6. David Geffen School of Medicine at UCLA; Los Angeles CA USA
7. Royal Victoria Hospital; McGill University Health Centre; Montreal Quebec Canada
8. Atlanta VA Medical Center; Atlanta GA USA
9. Emory University School of Medicine; Atlanta GA USA
10. Michael E. DeBakey VA Medical Center; Houston TX USA
11. Baylor College of Medicine; Houston TX USA
12. VA Pittsburgh Healthcare System; Pittsburgh PA USA
13. University of Pittsburgh School of Medicine; Pittsburgh PA USA
14. Washington DC VA Medical Center; Washington DC USA
15. George Washington University Medical Center; Washington DC USA
16. James J. Peters VA Medical Center and Mt. Sinai School of Medicine; New York NY USA
17. Mt. Sinai School of Medicine; New York NY USA
18. University of Pennsylvania School of Medicine; Philadelphia PA USA