aJohn's Hopkins University, Bloomberg School of Public Health, Baltimore, Maryland, USA
bUniversity of Illinois at Chicago School of Public Health, Chicago Illinois, USA
cSchool of Medical Sciences, University of Sydney, Sydney, New South Wales, Australia.
Received 2 February, 2010
Accepted 26 February, 2010
Correspondence to Ronald H. Gray, E4132, Johns Hopkins University, Bloomberg School of Public Health, 615 N Wolfe Street, Baltimore, MD 21205, USA. Tel: +1 410 955 7818; fax: +1 410 614 7386; e-mail: email@example.com