Professors Coggon and Newman Taylor1 correctly state that it is my opinion that the adverse effects of cigarette smoking vary markedly with only around 15–20% of smokers being affected, while the effects of coal mine dust are distributed much more evenly. They find my arguments unconvincing because Fletcher and coworkers’ “seminal longitudinal study into the natural history of COPD found that the presence of chronic bronchitis had no independent influence on the decline of the FEV₁.”2

I yield to none in my admiration for the work of Fletcher and his coworkers, but it needs to be pointed out that the men they selected were “aged 30 to 59 years since younger men were thought unlikely to have developed airflow obstruction by this age”. In this connection their assumption was incorrect. While non-smoking …