DIFFERENCES BETWEEN STUDIES IN REPORTED RELATIVE RISKS ASSOCIATED WITH SMOKING - AN OVERVIEW

REPORTED RELATIVE RISKS associated with smoking differ between studies ; these differences may reflect true biological differences between po pulations or may be research artifacts introduced by differences in fa ctors such as amount smoked or smoking duration. The authors reviewed the literature published before June 1992 on relative risks associated with smoking for heart disease, stroke, lung cancer, and chronic obst ructive lung disease. They quantified the effect of variables such as age, amount smoked, and smoking duration on reported relative risks. T he main reasons for the variation in reported relative risks were: mis classification of former smokers as never smokers, the use of mortalit y rate ratios rather than incidence rate ratios, a possible period eff ect suggesting increasing relative risks over time, and differences in the amount smoked. It is far more likely that these factors are respo nsible for the observed variation between studies than that the variat ions reflect true biological differences between populations. Using re lative risks from other studies is therefore justified in calculating a population attributable risk if the studies are carefully selected a nd address factors such as amount smoked and period effects.