As seen in Chapter 4, observational studies vary considerably in their sensitivity to hidden bias. The study of the study of coffee and myocardial infarction in §4.4.5 is sensitive to small biases while the studies of smoking and lung cancer in §4.3.3 or DES and vaginal cancer in §4.4.5 are sensitive only to biases that are many times larger. If sensitive to small biases, a study is especially open to the criticism that a particular unrecorded covariate was not controlled because, in this case, small differences in an important covariate can readily explain the difference in outcomes in treated and control groups. Still, all observational studies are sensitive to sufficiently large biases, and large biases have occurred on occasion; see §4.4.3. A sensitivity analysis shows how biases of various magnitudes might alter conclusions, but it does not indicate whether biases are present or what magnitudes are plausible.
KeywordsChildhood Cancer Chromosome Aberration Nuclear Testing Chromosome Damage Postmenopausal Estrogen
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