title: Case-control studies of the efficacy of cancer screening: overcoming bias from nonrandom patterns of screening.
abstract: A case-control study of the efficacy of cancer screening, like any other case-control study, must deal with potential confounding. There are 2 categories of confounding variables that pose special problems for studies of screening: (1) age and calendar time resulting from different temporal distributions of screening between cases and controls irrespective of whether the screening test leads to a reduction in mortality; and (2) the administration of other screening tests for the cancer in question when it is not clear whether the result of the other test had a bearing on the decision to order the test under study. We describe circumstances in which confounding from these sources can be dealt with satisfactorily by means of restriction or adjustment, and other circumstances in which it cannot.
authors.affiliation: University of Washington, Fred Hutchinson Cancer Research Center, Seattle, Washington 98195-7236, USA. nweiss@u.washington.edu
authors.forename: Noel S
authors.initials: NS
authors.lastname: Weiss
authors.forename: Preet K
authors.initials: PK
authors.lastname: Dhillon
authors.forename: Ruth
authors.initials: R
authors.lastname: Etzioni
mesh_terms: D000367:Age Factors; D015982:Bias; D016022:Case-Control Studies; D015986:Confounding Factors, Epidemiologic; D003955:Diagnostic Tests, Routine / Q000706:statistics & numerical data*; D006801:Humans; D008403:Mass Screening / Q000706:statistics & numerical data; D009369:Neoplasms / Q000175:diagnosis / Q000453:epidemiology*; D012107:Research Design; D012680:Sensitivity and Specificity; D013997:Time Factors; D016896:Treatment Outcome