1. School of Social Work, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
2. Department of Biostatistics, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
3. Department of Statistics, University of Pretoria, Pretoria, South Africa
4. Department of Statistics and Operations Research, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
5. PayPal, San Jose, CA, USA
6. Department of Epidemiology, University of Florida, Gainesville, FL, USA