1. RAND Corporation, Santa Monica, California.
2. Department of Veterans Affairs, Greater Los Angeles Healthcare System, Los Angeles, California.
3. Department of Medicine, David Geffen School of Medicine, Los Angeles, California.
4. Quest Diagnostics, West Hills, California.
5. Department of Pathology and Laboratory Medicine, David Geffen School of Medicine, Los Angeles, California.
6. Division of Laboratory Sciences and Standards, Centers for Disease Control and Prevention, Atlanta, Georgia.