Introduction A case-control study is designed to help determine if an exposure is associated with an outcome i. 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 free of the outcome.
Definition[ edit ] The case—control is a type of epidemiological observational study. 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.
If a larger proportion of the cases smoke than the controls, that suggests, but does not conclusively show, that the hypothesis is valid. The case—control study is frequently contrasted with cohort studieswherein exposed and unexposed subjects are observed until they develop an outcome of interest.
However, because the difference between the cases and the controls will be smaller, this results in a lower power to detect an exposure effect. As with any epidemiological study, greater numbers in the study will increase the power of the study.
Numbers of cases and controls do not have to be equal. In many situations, it is much easier to recruit controls than to find cases. Increasing the number of controls above the number of cases, up to a ratio of about 4 to 1, may be a cost-effective way to improve the study.
They have pointed the way to a number of important discoveries and advances.
The case—control study design is often used in the study of rare diseases or as a preliminary study where little is known about the association between the risk factor and disease of interest. Case—control studies are observational in nature and thus do not provide the same level of evidence as randomized controlled trials.
The results may be confounded by other factors, to the extent of giving the opposite answer to better studies. A meta-analysis of what was considered 30 high-quality studies concluded that use of a product halved a risk, when in fact the risk was, if anything, increased.
Case—control studies are therefore placed low in the hierarchy of evidence. Examples[ edit ] One of the most significant triumphs of the case—control study was the demonstration of the link between tobacco smoking and lung cancer, by Richard Doll and Bradford Hill. They showed a statistically significant association in a large case—control study.
Analysis[ edit ] Case—control studies were initially analyzed by testing whether or not there were significant differences between the proportion of exposed subjects among cases and controls.
It was later shown by Miettinen in that this assumption is not necessary and that the odds ratio of exposure can be used to directly estimate the incidence rate ratio of exposure without the need for the rare disease assumption.Differentiate between a nested case-control study and other case-control studies > Lecture Cross-Sectional Studies (Kanchanaraksa) Calculate odds ratios in matched and unmatched case-control studies.
Apply appropriate risk measures in public health planning Differentiate between the epidemiologic and the legal definition of causality. Field Epidemiology Manual.
Matching is a useful method to optimize resources in a case control study. (before the study, at the time of cases and control selection), with smaller sample sizes as compared to an unmatched sample with stratified analysis made "a posteriori".
Abstract. Matched case-control study designs are commonly implemented in the field of public health. While matching is intended to eliminate confounding, the main potential benefit of matching in case-control studies is a gain in efficiency. case-control study listen (kays-kun-TROLE STUH-dee) A study that compares two groups of people: those with the disease or condition under study (cases) and a very similar group of people who do not have the disease or condition (controls).
4 types of Matched case-control studies Definition Concordant pairs: pairs in which both the cases and controls were exposed, pairs in which both the cases and controls were unexposed:: Discordant pairs: Pairs in which the case was exposed and the control was not, Pairs in which the control was exposed and the case was not.
Case-control study designs are used to estimate the relative risk for a disease from a specific risk factor. The estimate is the odds ratio, which is a good estimate of the relative risk especially when the disease is rare. Case-control studies are useful when epidemiologists to investigate an.