Epidemiology
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The case-crossover study design is a popular analytic tool for estimating the effects of triggers of acute outcomes by environmental exposures. Although this approach controls for time-invariant confounders by design, it may allow for selection bias and confounding by time-varying factors. We conducted a simulation study of the sensitivity of the symmetric bidirectional case-crossover design to time-varying patterns in exposure and outcome. ⋯ Confounding results from a common temporal pattern in the exposure and the outcome time series, but can also be the result of patterns in exposure and outcome that, although asymptotically uncorrelated, are correlated at finite series lengths. All three biases are reduced by choosing shorter referent-spacing lengths. This effect is illustrated using data on air pollution and daily deaths in Chicago.
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Comparative Study
A comparison of the National Death Index and Social Security Administration databases to ascertain vital status.
We compared vital status follow-up by the National Death Index and the Social Security Administration for a cohort of breast cancer patients. Only the National Death Index allowed follow-up for subjects with an unknown Social Security number. ⋯ Subjects with inaccurate identifying information were more effectively followed up by the National Death Index. The National Death Index more accurately reported dates of death.
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This project signals an advance in cancer registration in the Middle East region. While it is too early to declare a major breakthrough, significant strides have been made toward establishing a basis for reliable information on the cancer burden at a population level and future collaborative efforts in cancer epidemiologic research and prevention.