Case control study

Infographic describing case control studies

A case-control study, also known as a case-control study or case-control study, is an epidemiological study, observational, analytical, in which the subjects are selected based on whether they have (cases) or do not have (control) a certain disease, or in general a certain effect. Once the individuals in each group have been selected, it is investigated whether or not they were exposed to a characteristic of interest and the proportion of those exposed in the case group is compared to that of the control group.

Types of case control studies

• Retrospective Case Control Study: All cases have been diagnosed before the study began.
• Prospective Case Control Study: Cases are diagnosed after the beginning of the study and new cases may be included for a certain time previously established.
• Population-based case control study: combines elements of the cohort study and cases and controls. A group of individuals is followed until the disease of interest appears in the same way as the cohort study. These cases are compared to a control group, sampled from the same population. Once all cases have been obtained and the controls are analyzed the type of previous or current exposure, such as in a case and control study.
• Anity Case Control Study: It is a case control study in which both cases and controls are taken from the population participating in a cohort study. Since data from this population are obtained over time, the possibility of selection biases and information is reduced, which are common in case control designs.

The use of the prospective and retrospective categories originally refers to the events in the life of the study participants and not to the way of collecting the information, for this reason the case-control studies were known from their origin as flashbacks. The notion of prospective or retrospective, referring to the collection of information and not to the events that occurred in the life of the patients, is a notion that appears later.

Technique of a case-control study

1. Select a sample of population with the disease or with the problem of study. Individuals of this sample are called cases.
2. Select a sample of the population at risk of getting sick but free from the problem disease, which will be the control group.
3. Measuring predictor variables, which are risk factors.

Advantages of case-control studies

1. They are useful to study rare events or such diseases.
2. They allow the study with relatively small sample sizes.
3. They demand little time in their execution.
4. Relatively cheap compared to cohort studies. Population-based designs are usually more expensive.
5. They provide odds ratio estimators.
6. They evaluate many risk factors for a disease or event.

Disadvantages of case-control studies

1. It is inefficient for the study of rare exposure effects.
2. It does not set the sequence of events of interest.
3. Possible case and control selection errors. This bias is lower in population base design.
4. Possible bias of survival.
5. They can only study a result variable (sickness).
6. They do not provide estimators of prevalence, incidence or attributable risk. In population base design, the incidence can be estimated.
7. They are inappropriate when the result of interest is not known at the beginning of the study or when the result is a continuous variable.