I thank Goh Phuay Yee and Tham Foong Yee for critical comments on the manuscript and the two anonymous reviewers for their very constructive and insightful comments.
Y.F.M. is supported by the Faculty of Medicine start-up fund (grant number R-183-000-104-112) and Provost start-up fund (grant number R-183-000-605-101), National University of Singapore.