TY - JOUR T1 - Joint action of smoking and asbestos exposure on lung cancer JF - Occupational and Environmental Medicine JO - Occup Environ Med SP - 494 LP - 495 DO - 10.1136/oem.59.7.494-a VL - 59 IS - 7 AU - F D K Liddell Y1 - 2002/07/01 UR - http://oem.bmj.com/content/59/7/494.2.abstract N2 - This subject has long been bedevilled by unwarrantable assumption and circular argument. Why should there be only two possible hypotheses of interaction (additive and multiplicative)? Theory expects multiplicativity; epidemiology can seldom reject this hypothesis; so theory is “accepted”, and deviations from multiplicativity must be explained away. Resolution is made especially difficult because the nature of the data imposes very large error; also it has to be assumed that the exposed smoked as many cigarettes as the unexposed, and that smokers and non-smokers were exposed equally.Thus the “comprehensive” review by Lee1 was to be welcomed. However, discrepancies, particularly with another review,2 demanded discussion: this letter is the result.From almost 40 “results” in 25 reports, Lee makes two selections to confirm the well known facts that asbestos can increase lung cancer risk in non-smokers and that the additive theory (of independent action) does not explain many of the data. Then, for 16 results, Lee calculates a statistic V; for an observed multiplicative interaction, V = 1. The weighted average V = 0.90 (95% CI: 0.67 to 1.20) leads to Lee's conclusion.1 Repair of (acknowledged) imperfections (one misquoted result; two incorrect omissions) reduced V only slightly, to 0.83 (95% CI: 0.63 to 1.08); for nine cohorts and nine case–referent studies, respectively, V = 0.63 and 1.08, a “significant” difference (p = 0.049).There are, however, other imperfections: two cohorts3,4 broke the rule of independence; in another,5 asbestos had a minuscule (protective) effect on lung cancer … ER -