We would like to clarify some of the issues raised by Professor Knutsson (Occup Environ Med 2008;65:152) in his recent commentary concerning our article “Shift work, confounding and death from ischaemic heart disease”.1 Firstly, it is not true that previously “a similar study was carried out at the same factory”. As we state in our article, the subjects of the present study were from a different cohort from that investigated by McNamee et al2 in 1996. The cohorts of the two studies had the same employer but correspond to two different …