A case-control study is a type of observational study in which two existing groups differ in the results identified and compared on the basis of some supposed causal attributes. Case-control studies are often used to identify factors that may contribute to medical conditions by comparing subjects with "disease" ("case") conditions with patients who do not have conditions/diseases but are otherwise similar ("control"). They require fewer resources but provide less evidence for causal inferences than randomized controlled trials. We only get an odds ratio from a case control study which is a lower association strength measure compared to relative risk.
Video Case-control study
Definitions
Case control is an observational type of epidemiological study. An observational study was a study in which subjects were not randomized for exposed or unexposed groups, but subjects were observed to determine both their exposure and the status of their results and the exposure status thus unspecified. by researchers.
Porta Epidemiological Dictionary defines case-control studies as: an observational epidemiological study of people with interesting diseases (or other outcome variables) and appropriate control groups of people without disease (comparison group, reference group). The potential relationship of suspected risk factors or attributes to this disease is examined by comparing the sick and non-contemplating subject to how often factors or attributes are present (or, if quantitative, attribute levels) in each group (diseased and disregarded). "
For example, in a study that attempted to show that people who smoked ( attribute ) were more likely to be diagnosed with lung cancer (outcome ), the case > will be a person with lung cancer, control will be a person without lung cancer (not necessarily healthy), and some of each group will become smokers. If the proportion of cigarette cases is greater than the control, it shows, but does not show conclusively, that the hypothesis is valid.
Case-control studies are often contrasted with cohort studies, in which exposed and unexposed subjects are observed until they develop interesting results.
Group control options
Control does not need to be in good health; the inclusion of sick people is sometimes appropriate, since the control group must represent those at risk of being a case. Control should come from the same population as the case, and their choice should be independent of the interest exposure.
Controls can carry the same disease with the experimental group, but from other classes/severity, therefore different from the desired result. However, since the difference between case and control will be smaller, this results in lower power to detect the lighting effects.
As with epidemiological studies, a larger amount in this study will increase the strength of the study. The number of cases and controls should not be the same. In many situations, it is much easier to recruit control than to find cases. Increasing the number of controls over the number of cases, to a ratio of about 4 to 1, may be a cost-effective way to improve research.
Maps Case-control study
Strengths and weaknesses
Case-control studies are a relatively inexpensive and often used type of epidemiological research that can be done by small teams or individual researchers in a single facility in a way that can not be done by a more structured experimental study. They have pointed the way to a number of important discoveries and progress. The case-control study design is often used in the study of rare diseases or as a preliminary study in which little is known about the relationship between risk factors and an attractive disease.
Compared with prospective cohort studies, they tend to be cheaper and shorter in duration. In some situations, they have greater statistical power than cohort studies, which must often wait for the number of 'sufficient' diseases to increase.
The case-control study is observational and thus does not provide the same level of evidence as randomized controlled trials. The results may be confused by other factors, as far as providing the opposite answer for better study. A meta-analysis of what counts 30 high-quality studies concludes that the use of products is half the risk, when in fact the risks, if any, increase. It may also be more difficult to establish the timeline of disease outcome exposure in case-control setting studies than in a prospective cohort study design where exposure is ensured prior to following the subject from time to time to ascertain the status of their outcomes. The most important disadvantages in case-control studies are related with difficulty obtaining reliable information about the status of individual exposure over time. The case control study is therefore placed low in the hierarchy of evidence.
Example
One of the most significant triumphs of a case-control study was the demonstration of a link between tobacco smoking and lung cancer, by Richard Doll and Bradford Hill. They showed statistically significant associations in large case-control studies. Opponents argued for years that this type of study could not prove causation, but the end result of the cohort study confirmed the causal relationship suggested by the case-control study, and it is now accepted that smoking is the cause of about 87% of all lung cancer deaths lung in the US.
Analysis
The case-control study was initially analyzed by testing whether there was a significant difference between the proportion of subjects exposed between cases and controls. Furthermore, Cornfield suggests that, when the illness of flower yields is rare, it is likely that the exposure ratio can be used to estimate relative risk (see rare disease assumptions). It was then demonstrated by Miettinen in 1976 that this assumption was not necessary and that the ratio of exposure possibilities could be used to directly estimate the ratio of the incidence rate of exposure without the need for rare disease assumptions.
See also
- nested case-control study
- Retrospective cohort study
- Randomized controlled trial
References
Further reading
- Stolley, Paul D.; Schlesselman, James J. (1982). Case control study: design, behavior, analysis . Oxford [Oxfordshire]: Oxford University Press. ISBN: 0-19-502933-X. (Still a very useful book, and a great place to start, but now a little out of date.)
External links
- Wellcome Trust Case Control Consortium
- authors of case studies - National center of observational studies
Source of the article : Wikipedia
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