Epidemiology in Practice: Case-Control Studies


example of a case control study

A case-control study is usually conducted before a cohort or an experimental study to identify the possible etiology of the disease − It costs relatively less and can be conducted in a shorter time For a given disease, a case-control study can investigate multiple exposures (when the real exposure is not known) A case-control study is. Dec 06,  · Case-control studies. Case-control studies are retrospective. They clearly define two groups at the start: one with the outcome/disease and one without the outcome/disease. They look back to assess whether there is a statistically significant difference in the rates of exposure to a defined risk factor between the groups. Example Conducted a case-control study to determine if there is an association between colon cancer and diet (high fat diet, coffee). – Cases were all confirmed colon cancer cases in CA in – Controls were a sample of CA residents without colon cancer.

Case Control - Study Design

Specifically, among those potentially exposed to an agent or factor, it is the proportion who develop disease. A cohort study design works well in these circumstances. However, in most outbreaks the population is not well defined, and cohort studies are not feasible. A good example of this is an actual outbreak of hepatitis A that occurred in Marshfield, MA in Excerpts from introduction of the report by the Massachusetts Department of Health.

Within a short period of time 20 cases of hepatitis A were identified in the Marshfield area. The epidemic curve suggested a point source epidemic, and the spot map showed the cases to be spread across the entire South Shore of Massachusetts, although the pattern suggested a focus near Marshfield. Hypothesis-generating interviews resulted in five food establishments that were candidate sources. Moreover, the disease was rare, so that even if they interviewed a sample of patrons at each of example of a case control study restaurants, it is most likely that few, if any would have had recent hepatitis, even from the responsible restaurant.

In a situation like this a case-control design is a much more efficient option. The investigators identified as many cases as possible 19 agreed to answer the questionnaireand they selected a sample of 38 non-diseased people as a comparison group the controls. In this case, the "controls" were non-diseased people who were matched to the cases with respect to age, gender, and neighborhood of residence.

Investigators then ascertained the prior exposures of subjects in each group, focusing on food establishments and other possibly relevant exposures they had had during the past two months. However, one can calculate the odds of disease in exposed and non-exposed subjects, and these can be expressed as an odds ratio, which is a good approximation of a example of a case control study ratio in a situation like this, i. An odds ratio can be computed for each of the possible sources.

Consider the following example:. These odds are quite similar, example of a case control study, and the odds ratio is close to 1. The odds ratio can be interpreted the same way as a risk ratio. This suggests that patrons of Ron's Grill had 75 times the risk of being a case compared to those who did not eat at Ron's. The other three restaurants that had been suspects had odds ratios that were close to 1.

This certainly provides strong evidence that a Ron's Grill was the source of the outbreak, and further investigation confirmed that one of the food handlers at Ron's had recently had a subclinical case of hepatitis A.

In case-control studies, one of the most difficult decisions is how to select the the controls. Ideally they should be non-diseased people who come from the same source population as the cases, example of a case control study, and, aside from their outcome status, they should be comparable to the cases in order to avoid selection bias. Note that in the Marshfield case-control study the controls were selected in a way to ensure that they were comparable with respect to age and gender and lived in similar neighborhoods.

For more information about the conduct and analysis of case-control studies, please see the online modules on:. All Rights Reserved. Date last modified: May 3, Wayne W. Outbreak Investigations. Contents All Modules. In addition, a case of hepatitis A in a Plymouth resident, example of a case control study, employed in Marshfield, was reported. For more information about the conduct and analysis of case-control studies, please see the online modules on: Link to module giving an overview of Analytical Studies Link to module example of a case control study Case-Control Studies For more information on developing questionnaires for outbreak studies, see: Link to information on developing a example of a case control study return to top previous page next page.


Case–control study - Wikipedia


example of a case control study


A case-control study is designed to help determine if an exposure is associated with an outcome (i.e., 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 Cited by: One of the most widespread types of study nowadays is a case-control study. The purpose of the case-control study is to determine the causes of the onset and spread of the disease. In the case-control studies, the probability of the existence of a causal relationship is based not on the different incidence of morbidity, but on the different prevalence (occurrence) of the predicted risk factor. Case–control studies are therefore placed low in the hierarchy of evidence. Examples. 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.