Our results indicate greater positional errors for rural addresses compared with town addresses. Using a commercial firm did not improve accuracy compared with our in-house method. The effect of geocoding errors on exposure classification will depend on the spatial variation of the exposure being studied.

Results are described from four epidemiologic studies in the United States which used random digit dialing in over 30,000 households to identify controls from the general population for use in case-control studies. Methods and problems in telephone sampling are discussed. It is concluded that if complete population rosters are unavailable and if the population to be sampled has the high rates of telephone ownership typical of much of the United States, telephone-based sampling can yield a nearly random sample of the individuals in a population, often at much less expense than can dwelling-based sampling.

A key assumption made when using a validation study to correct an estimate of relative risk for bias due to misclassification or measurement error is that the available measure, known to have error but nonetheless used routinely in the main study, is compared to a gold standard measured without error. In most epidemiologic applications, the putative gold standard is in fact measured with error. The effect of the violation of the assumption on the corrected estimate depends on the magnitudes of the errors in the two measures and on their correlation. In particular, when the errors are negatively correlated, independent, or weakly positively correlated, the corrected estimate will tend to overcorrect beyond the true value.

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Background Cigarettes are well known to cause cancer, but less is known about the risks of other tobacco products and use of more than one product. Methods We examined cancer incidence in relation to exclusive use of six tobacco products (cigarettes, other combustibles (pipe, cigar, cigarillo), and smokeless tobacco (chewing tobacco, snuff)) in the Agricultural Health Study. We also examined the added cancer risks associated with use of cigarettes and other tobacco products. Results In our study population of 84,015, ever use of smokeless tobacco was higher than the general United States population, while cigarette use was lower and other combustible product use was about the same. The strongest associations for exclusive ever use were for lung cancer (cigarettes hazard ratio (HR)=15.48, 95% confidence interval (CI): 11.95, 20.06; other combustible tobacco HR=3.44, 95% CI: 1.53, 7.71; smokeless tobacco HR=2.21, 95% CI: 1.11, 4.42). Compared to exclusive cigarette smokers, cigarette smokers who additionally ever-used another combustible product had higher risks of smoking related cancers (HR=1.16, 95% CI: 1.04, 1.30), especially among those who smoked cigarettes for more than 15 years. Conclusion and Impact Cigarette smokers who additionally ever used smokeless tobacco had cancer risks similar to exclusive cigarette smokers. Users of cigarettes and other combustible tobacco may have higher risks of certain cancers than exclusive cigarette users.