1. Department of Statistics and Applied Probability; National University of Singapore; Singapore 117946 Singapore
2. Duke-NUS Graduate Medical School; Singapore 169857 Singapore
3. Singapore Eye Research Institute; Singapore
4. Department of Statistics and Biostatistics; University of North Carolina; Chapel Hill North Carolina U.S.A.
5. Department of Epidemiology; University of North Carolina; Chapel Hill North Carolina U.S.A.