Observational Studies: Cohort and Case-Control Studies

 

retrospective case control study

Aug 22,  · Retrospective Case-Control Study. Case-control studies involve two groups of people: people who have the disease (cases) and those who do not (controls). A retrospective case-control uses these two groups and looks back to the past for data and possible risk factors. 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: A retrospective case control study is one that uses existing data to compare two groups. For example, people who have developed a disease might be compared with a group of people who have not. The researcher will look at whether there is any difference in the two groups in their previous exposure to possible risk factors.


Epidemiology in Practice: Case-Control Studies


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. Then, look back in time to learn which subjects in each group had the exposure scomparing the frequency of the exposure in the case group to the control group.

By definition, a case-control study is always retrospective because it starts with an outcome then traces back to investigate exposures.

When the subjects are enrolled in their respective groups, the outcome of each subject is already known by the investigator. Case-control studies have specific advantages compared to other study designs.

They are comparatively quick, inexpensive, and easy. They are particularly appropriate for 1 investigating outbreaks, and 2 studying rare diseases or outcomes. An example of 1 would be a study of endophthalmitis following ocular surgery. When an outbreak is in progress, answers must be obtained quickly. Retrospective case control study example of 2 would be a study of risk factors for uveal melanoma, or corneal ulcers.

Since case-control studies start with people known to have the outcome rather than starting with a population free of disease and waiting to see who develops it it is possible to enroll a sufficient number of patients retrospective case control study a rare disease.

The practical value of producing rapid results or investigating rare outcomes may outweigh the limitations of case-control studies. Because of their efficiency, they may also be ideal for preliminary investigation of a suspected risk factor for a common condition; conclusions may be used to justify a more costly and time-consuming longitudinal study later. Consider a situation in which a large number of cases of post-operative endophthalmitis have occurred in a few weeks.

The case group would consist of all those patients at the hospital who developed post-operative endophthalmitis during a pre-defined period. Within what period of time after operation will the development of endophthalmitis qualify as a case — one day, one week, or one month?

Will endophthalmitis have to be proven microbiologically, or will a clinical diagnosis be acceptable? Clinical criteria must be identified in great detail. If microbiologic facilities are available, how will patients who have negative cultures be classified? Controls should be chosen who are similar in many ways to the cases. The factors e. The selected control group must be at similar risk of developing the outcome; it would not be appropriate to compare a group of controls who had traumatic corneal lacerations with cases who underwent elective intraocular surgery.

In our example, controls could be defined as patients who underwent elective intraocular surgery during the same period of time.

Although controls must be like the cases in many ways, it is possible to over-match. Over-matching can make it difficult to find enough controls. Also, once a matching variable has been selected, it is not possible to analyse it as a risk factor. Matching for type of intraocular surgery e. An important technique for adding power to a study is to enroll more than one control for every case. For statistical reasons, however, there is little gained by including more than two controls per case.

After clearly defining cases and controls, decide on data to be collected; the same data must be collected in the same way from both groups.

Care must be taken to be objective in the search for past risk factors, especially since the outcome is already known, or the study may suffer from researcher bias. Although it may not always be possible, it is important to try to mask the outcome from the person who is collecting risk factor information or interviewing patients.

Sometimes it will be necessary to interview patients about potential factors such as history of smoking, diet, use of traditional eye medicines, etc. It may be difficult for some people to recall all these details accurately. Furthermore, patients who have the outcome cases are likely to scrutinize the past, remembering details of negative exposures more clearly than controls.

This is known as recall bias. Anything the researcher can do to minimize this type of bias will strengthen the study. In the analysis retrospective case control study, calculate the frequency of each of the measured variables in each of the two groups. As a measure of the strength of the association between an exposure and the outcome, case-control studies yield the odds ratio. An odds ratio is the ratio of the odds of an exposure in the case group to the odds of an exposure in the control group.

It is important to calculate a confidence interval for each odds ratio. A confidence interval that includes 1. An odds retrospective case control study without a confidence interval is not very meaningful. These calculations are usually made with computer programmes e, retrospective case control study.

Case-control studies cannot provide any information about the incidence or prevalence of a disease because no measurements are made in a population based sample. Another use for case-control studies is investigating risk factors for a rare disease, such as uveal melanoma.

In this example, cases might be recruited by using hospital records. Patients who present to hospital, however, may not be representative of the population who get melanoma. If, retrospective case control study, for example, women present less commonly at hospital, bias might occur in the selection of cases.

The selection of a proper control group may pose problems. A frequent source of controls is patients from the same hospital who do not have the outcome. However, hospitalised patients often do not represent the general population; they are likely to suffer health problems and they have access to the health care system. An alternative may be to enroll community controls, people from the same neighborhoods as the cases.

Sometimes researchers enroll multiple control groups. These could include a set of community controls and a set of hospital controls. Matching controls to cases will mitigate the effects of confounders.

A confounding variable is one which is associated with the exposure and is a cause of the outcome. Case-control studies may prove an association but they do not demonstrate causation.

Consider a case-control study intended to establish retrospective case control study association between the use of traditional eye medicines TEM and corneal ulcers. TEM might cause corneal ulcers but it is also possible that the presence of a corneal ulcer leads some people to use TEM.

The temporal relationship between the supposed cause and effect cannot be determined by a case-control study. Case-control studies are sometimes less valued for being retrospective. However, they can be a very efficient way of identifying an association between an exposure and an outcome. Sometimes they are the only ethical way to investigate an association. If care is taken with definitions, selection of controls, and reducing the potential for bias, case-control studies can generate valuable information, retrospective case control study.

National Center for Biotechnology InformationU. Journal List Community Eye Health v, retrospective case control study. Community Eye Health. Author information Copyright and License information Disclaimer. This article has been cited by other articles in PMC, retrospective case control study. Introduction A case-control study is retrospective case control study to help determine if an exposure is associated with an outcome i.

Advantages of Case-Control Studies Case-control studies have specific advantages compared to retrospective case control study study designs. Cases Consider a situation in which a large number of cases of post-operative retrospective case control study have occurred in a few weeks. The definition of a case needs to be very specific: Within what period of time retrospective case control study operation will the development of endophthalmitis qualify as a case — one day, one week, retrospective case control study, or one month?

How will sterile inflammation be differentiated from endophthalmitis? Controls Controls should be chosen who are similar in many ways to the cases. Matching Cases and Controls Although controls must be like the cases in many ways, it is possible to over-match. Collecting Data After clearly defining cases and controls, decide on data to be collected; the same data must be collected in the same way from both groups.

Analysis; Odds Ratios and Confidence Intervals In the analysis stage, calculate the frequency of each of the measured variables in each of the two groups. Risk Factors and Sampling Another use for case-control studies is investigating risk factors for a rare disease, such as uveal melanoma.

Confounders Matching controls to cases will mitigate the effects of confounders. Comment Case-control studies may prove an association but they do not demonstrate causation. Advantages Disadvantages can obtain findings quickly can often be undertaken with minimal funding efficient for retrospective case control study diseases can study multiple exposures generally requires few study subjects cannot generate incidence data subject to bias difficult if record keeping is either inadequate or unreliable selection of controls can be difficult.

Open in a separate window. Recommended Reading 1. Evaluation of prior primary malignancy as a determinant of uveal melanoma. A case-control study.

Host factors, UV radiation, and risk of uveal melanoma. Arch Ophthalmol. Ophthalmic Epidemiology. Grisso JA. Making comparisons. For information about Epi Info Version 6a word processing, database, and statistics program for epidemiology on microcomputers, please contact Centers for Disease Control and Prevention, Atlanta, GA Retrospective case control study Center Support Center.

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Retrospective Case Control Study - EUPATI

 

retrospective case control study

 

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. Keywords: observational studies, case-control study, cohort study, Instead, retrospective cohort studies are better indicated given the timeliness and inexpensive nature of the study design. Retrospective cohort studies, also known as historical cohort studies, are carried out at the present time and look to the past to examine medical Cited by: Retrospective studies may need very large sample sizes for rare outcomes. Comparison with case-control studies. While retrospective cohort studies try to compare the risk of developing a disease to some already known exposure factors, a case-control study will try to determine the possible exposure factors after a known disease incidence. Both.