RT Journal Article SR Electronic T1 Authors’ reply JF Occupational and Environmental Medicine JO Occup Environ Med FD BMJ Publishing Group Ltd SP 856 OP 856 VO 64 IS 12 A1 D S-Q Koh A1 G C-H Koh YR 2007 UL http://oem.bmj.com/content/64/12/856.2.abstract AB