In Reply: Dr Dowdy points out that a substantial proportion of the person-time in our study occurred among former smokers. As individual former smokers cannot change their status to never-smokers, he questions whether our presentation of PARs is meaningful. Although individual former smokers cannot become never-smokers, it is conceivable to eliminate cigarette smoking at the population level. The first use of the PAR was by Levin in 1953 for the purpose of estimating the burden of lung cancer caused by ever smoking,1 and this approach has been used many times subsequently, including the US Surgeon General's Report on the Health Consequences of Smoking.2
Freedman ND, Silverman DT, Abnet CC. Tobacco Smoking and Bladder Cancer—Reply. JAMA. 2011;306(20):2216–2217. doi:10.1001/jama.2011.1718
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