Smoking and lung cancer: causality, Cornfield and an early observational meta-analysis

As has been noted before, we receive a surprising number of papers that present data on smoking and lung cancer with a contrived air of originality and excitement. This is the first time that the link has been shown in this particular subgroup of our population! Well, the second perhaps, but we could adjust for more confounders. We have none of these papers in this issue of the IJE—or in fact in any issue, unless under the influence of influenza or a hangover we allow our guard to slip. However, we are lucky enough to publish the second article on smoking and lung cancer under our editorship that is indeed exciting and original. The first of these was our translation into English of Schairer and Schöniger’s pioneering case–control study carried out in Germany in the early 1940s. The second is a reprint to mark 50 years after the initial publication of Jerome Cornfield and colleagues’ ground-breaking account of how causal inference could be applied to observational data on smoking and lung cancer, with a series of admiring commentaries that place it in context and discuss how well its ideas have stood the test of time (pretty well is the general consensus). As a trained historian—Cornfield’s (Figure 1) initial degree and graduate study were in history —we hope he would appreciate the often historical focus of material in the IJE. It proved very difficult to select which of his important papers to reprint. A strong case could be made for his 1956 paper ‘A statistical problem arising from retrospective studies’, generally noted for its discussion of how under certain assumptions the odds ratio is a fairly good approximation of the relative risk. This paper also presented an early meta-analysis (although Cornfield did not call it this) of 14 case–control studies of smoking and lung cancer the data for which were attributed to a 1954 paper by Cornfield’s ex-boss, Harold Dorn. The Schairer and Schöniger case–control study was included in this meta-analysis as study number 2, as was an earlier German study and several subsequent ones. The studies often said to be the pioneers—Wynder and Graham for North Americans and Doll and Hill for Europeans—were studies 6 and 8, respectively, indicating their position in the ordering by date of publication. Cornfield pointed out that while ‘methods exist for deciding whether the differences among the studies are significant, this is not a question of great interest. Rather we should like an interval estimate of the extent to which they do differ’. Focusing on 10 studies which appeared to be attempting to estimate the same parameter (which lead to Wynder and Graham’s study being excluded) he concluded that the relative risk lay between 5.0 and 7.2, pointing out that this would be considerably larger if the risk in just cigarette smokers could be examined. Reflecting one of the limitations of meta-analysis of published data, only the risk in smokers of any tobacco product vs non-smokers could be estimated. Interestingly, through Cornfield’s paper, the data on these 14 case–control studies of smoking and lung E-mail: ije-editorial@bristol.ac.uk Figure 1 Reproduced with permission of Johns Hopkins Bloomberg School of Public Health Published by Oxford University Press on behalf of the International Epidemiological Association