Introduction in case-control studies, the role of adjustments for bias, and in particular the role of matching, has been extensively debated (1-7) however the absence of a formal statement of the problem has led to disagreements, confusion, and occasionally to erroneous conclusions. A case-control study is designed to help determine if an exposure is associated with an outcome (ie, disease or condition of interest) in theory, the case-control study can be described simply first, identify the cases (a group known to have the outcome) and the controls (a group known to be.
Berkesonian bias is a bias introduced in hospital based case-control studies, due to varying rates of hospital admissions as the potential for selection bias is likely to be less of a problem in population based case-control studies, neighbourhood controls may be a preferable choice when using cases from a hospital or clinic setting. We discuss two classes of bias that arise in case–control studies, selection bias and information bias a third source of bias, confounding, is not considered in this article selection bias arises either when cases in the study sample are not representative of cases arising from the source population (“study base”) or when controls are.
Case control studies are observational because no intervention is attempted and no attempt is made to alter the course of the disease the goal is to retrospectively determine the exposure to the risk factor of interest from each of the two groups of individuals: cases and controls (also called recall bias) a case-control study was.
In a case-control study selection bias occurs when subjects for the control group are not truly representative of the population that produced the cases remember that in a case-control study the controls are used to estimate the exposure distribution (ie, the proportion having the exposure) in the population from which the cases arose. In case-control studies, selection bias can occur in the selection of cases if they are not representative of all cases within the population, or in the selection of controls if they are not representative of the population that produced the cases. Full text full text is available as a scanned copy of the original print version get a printable copy (pdf file) of the complete article (15m), or click on a page image below to browse page by page links to pubmed are also available for selected references.
The application of therapeutic-trial principles to improve the design of epidemiologic research: a case-control study suggesting that anticoagulants reduce mortality in patients with myocardial infarction. We discuss two classes of bias that arise in case–control studies, selection bias and information bias a third source of bias, confounding, is not considered in this article. The above study was a population based case-control study, with all babies born with a cleft lip in norway between 1996 and 2001 identified as cases and with a sample of controls selected at random from the norwegian medical birth registry for the same period.