Nnselection of controls in case-control studies pdf merger

A particular problem inherent in case control studies is the selection of a comparable control group. In theory, every casecontrol study takes place within a cohort, although. All casecontrol studies are done within some cohort defined or not in reality, the distinction between cohort and casecontrol designs is artificial ideally, cases and controls must represent a fair sample of the underlying cohort or study base toughest part of case control design. Casecontrol studies start with the outcome and look backward for the exposure, unlike cohort studies, which start from the exposure and look forward for the outcome. In view of this there are two key principles that should be followed in selecting controls. Topics covered include matching, control case ratio, choice of nested case. In unmatched casecontrol studies, having roughly equal numbers of cases and controls is most efficient if costs are similar for cases and controls. Second, controls should come from the same population as the cases, and their selection should be independent of the exposures of interest. Apr 30, 20 casecontrol studies need to be designed very carefully the complexity of their design is often not appreciated by investigators, and so many poorquality studies are conducted. Yes no statin 20 1,000 1,020 no statin 80 9,000 9,080 100 10,000 10,100 rr 20 1,020 80 9,080 2.

Note that it is not possible to estimate the incidence of disease from a case control study unless the study is population based and all cases in a defined population are obtained. Both exposure and outcome have occurred before the start of the study. For example, we may enroll 105 cases and 178 controls. Finding controls for case control studies david a grimes, kenneth f schulz use of control comparison groups is a powerful research tool. Compare diseased with not diseased on previous exposures. The questions in this checklist are designed to identify the main features that should be present in a welldesigned study. A coordination and configuration unit controls which mode is used, i. Analytic methods for non matched case control studies include. Controls are used to estimate the prevalence of exposure in the population which gave rise to the cases. Case control studies can study multiple risk factorsexposures 4. In nested case control studies where the exposure level of each subject is needed to measure at an additional cost, e. Cases and controls are registered in a cohort study. One may start with a group of people with a known exposure and a comparison. Number of controls per case increases statistical efficiency power ability to detect associations 4.

When case control studies were first developed, most were conducted retrospectively, and it is sometimes assumed that the raredisease assumption applies to all case control studies. These principles also apply to the design of cohort studies, as would be expected since the casecontrol design is simply an efficient sampling technique to measure exposuredisease associations in a cohort or study base. Exposures are determined and compared for individuals in each group. Begin with the outcome and look for features of people who share that outcome, then compare characteristics with subjects who do not. Controls can be taken from known or unknown study populations. Traditionally, case control studies have been viewed as an alternative to cohort studies in which individuals were selected on the basis of whether or not they had the disease outcome of interest, with investigators then comparing exposure history between those with the disease the cases and those free of the disease the controls. Pdf control selection methods in recent casecontrol. For example, cases can be contrasted with matched controls to adjust for multiple genetic. They are useful for studying outcomes diseases that take a long time to develop, e. For epidemiologic matched case control study designs, sas programs were developed to match cases persons with diseaseevent of interest to controls comparison group of persons without disease. Matching is often used in casecontrol control studies to ensure that the cases and controls are similar in certain characteristics, and it is a useful technique to. Casecontrol studies begin at the end outcome is the basis to select the comparison groups they test hypotheses concerning the association and magnitudes of a relationship between outcomes and exposures the strength of association is measured by an odds ratio or which is a good proxy for a relative risk when disease is rare. An observational study is a study in which subjects are not randomized to the exposed or unexposed groups, rather the subjects are observed in order to determine both their exposure and their outcome status and the exposure status is thus not determined by the researcher. Dec 29, 2016 casecontrol studies a case control study involves two populations cases and controls and has three distinct features.

Instead of looking at the probability of disease given exposure, look at the probability of exposure given disease. One also has the possibility in all casecontrol studies that patient. In casecontrol studies the measure is called the odds ratio may be used on its own or as an estimate the relative risk calculating risk in casecontrol studies cohort studies calculate relative risk to calculate relative risk must have incidence in a casecontrol study do not have incidence just selected cases and controls. Mandep a synthesis of classical and recent thinking on the issues involved in selecting controls for case control studies is presented in this and two companion papers s. Case control studies are prone to selection and recall bias i. A primary concern of investigators who design casecontrol studies is confounding a distortion of the effect of the exposure of interest due to the effects of an extraneous variables. Case control studies e r i c n o t e b o o k s e r i e s case control studies are used to determine if there is an association between an exposure and a specific health outcome.

Matching controls to cases on the basis of established risk factors for the outcome of interest is a common practice in casecontrol investigations. Langche zeng george washington university, washington, district of columbia, u. Analysis of case control studies the odds ratio or is used in case control studies to estimate the strength of the association between exposure and outcome. One may start with a group of people with a known exposure and a comparison group control group without the exposure and follow them through time to see what outcomes result, but this does not constitute a casecontrol study.

This work is licensed under a creative commons attribution. Cases and controls are patients who are hospitalized or outpatients. Data quality control in genetic casecontrol association. Design, conduct, and analysis of case control studies. Introduction to study designs casecontrol studies health. Design and analysis of casecontrol studies uc davis health. Pdf combining matched and unmatched control groups in. The first is a non matched case control study in which we enroll controls without regard to the number or characteristics of the cases. Case control studies have been used to estimate the odds ratios ors for involvement in road traffic accidents.

Casecontrol studies, inference in gary king harvard university, cambridge, massachusetts, u. The casecontrol is a type of epidemiological observational study. Multiple control groups in case control studies are used to control for different sources of confounding. Shortcomings in study design and errors in genotype calling have the potential to introduce systematic biases into genetic case control association studies. Learn vocabulary, terms, and more with flashcards, games, and other study tools. A pancreatic cancer case control study was conducted in the minneapolisst. The case control study is designed to compare cases to controls with respect to a currently or previously assessed exposure variable of interest. Gehlbach, interpreting the medical literature, 1993 casecontrol studies start with a disease, and work backward to find associations between exposures and the disease. However, it actually only applies to those case control studies in which controls are sampled only from the non diseased rather than the whole population. Definition of a case control study a study in which cases of disease are identified, and then a sample of the population that produced the cases is identified the controls. Statin 20 20 no statin 80 180 100 200 rr or 2020 180 80 2. Therefore, the ideal control group would comprise a random sample from the general population that gave rise to the cases. A casecontrol study of pancreatic cancer and cigarettes. Family members were interviewed about the subjects usage of cigarettes, alcohol, coffee, and other dietary factors in the two years prior to death cases, n 212 or prior to interview controls, n 220.

As noted above, it is always useful to think of a case control study as being nested within some sort of a cohort, i. In case control studies, controls estimate the frequency of an exposure in the population under study. Introduction classic or cumulative casecontrol sampling designs do not admit inferences about quantities of interest other. In this study design, the number of controls does not necessarily equal the number of cases. It uses a control or comparison group to support or refute an inference. An advantage of case control studies is that they can be used to study infrequent disease and outcome events or diseases with long latency periods. Several design options available in the planning stage of case control studies are examined. We assessed control selection methods used in recently published case control studies for methodological and resource issues to determine if a standard approach could be identified.