Question

a study regarding risk factors of cervical cancer a case of control study

Answer 1

Case control study is a study which compares who have a disease or outcome of interest (cases) with patients who do not have disease or outcome(controls) and look back retrospectively to compare how frequently the exposure to a risk factor is present in each group to determine the relationship between risk factor and disease. Case control studies are also known as "retrospective disease" or "case referent studies". Case control studies are observational because no intervention is attempted and no attempt is made to alter tue course of disease.

Design of case control study:-

1. A clearly defined hypothesis- Like all epidemiological studies it is important to start case control study by formulating a clearly defined hypothesis. It is important that the case definition is clearly defined at the start of the investigation and to make sure all the cases belong to same diagnostic criteria. The sources of case should also be clearly defined.
2. Selection of case-   

• Incident cases- comprises cases newly diagnosed at a defined period of time. It is preferential because the recall of past exposure will be more relevant in newly diagnosed cases.
• Prevelant case- comprise individuals who have had the outcome under investigation for some time. The use of prevalent cases may give rise to recall bias as prevalent cases may be less likely to accurately report past exposures.

3) Sources of cases- it can be hospitals, clinics, GP registered or population based. Population based is less preferred because it is expensive and hard to control.

4) Selection of control- the ideal control group would comprise a random sample from the general population that gave rise to the cases. However, this is not always possible in practice. The goal is to select individuals in whom the distribution of exposure status would be the same as that of the cases in the absence of an exposure disease association. That is, if there is no true association between exposure and disease, the cases and controls should have the same distribution of exposure. The source of controls is dependent on the source of cases. In order to minimize bias, controls should be selected to be a representative sample of the population which produced the cases. For example, if cases are selected from a defined population such as a GP register, then controls should comprise a sample from the same GP register.

5) Measuring of exposure status- Exposure status is measured to assess the presence or level of exposure for each individual for the period of time prior to the onset of the disease or condition under investigation when the exposure would have acted as a causal factor.

Please follow the above mentioned design to perfom your case study.