Case-control study

A case- control study is a form of epidemiological studies in medicine. This is a retrospective analysis of a sample consisting of diseased individuals ( cases ), and a sample consisting of healthy individuals (control). For both groups, it is then determined whether, in the past exposure to potential risk factors was present. A significant difference between the two groups is a correlation between risk factor and disease. In no case, however, one can infer a cause / effect relationship. A retrospective study arrangement as the case -control study is particularly suited to uncovering the causes of rare diseases. This person to be examined, which have a certain disease, and compared to suitable control groups. The disease is searched in retrospect for a cause.

Selection of cases

In a case-control study, the cases are selected on the basis of the disease and not the exposure. In the selection there are different sources such as hospital patients or patients from the low- Let range. To prevent the discovered risk factors are due solely to a special hospital, it is advisable to select cases from different hospitals or provinces. It must also in the selection of cases to be determined whether new ( incidental ) or existing ( prevalent ) cases are included. In case -control studies is recommended to include incidence cases, because there is in prevalence cases, the risk that the risk factor is discovered indicating a correlation with survival and not on the basis of the disease. For example, if the number of patients should die shortly after diagnosis, these patients will be under-represented in the study with prevalent cases and ultimately distort the result. For incident cases, however, it should be noted that the period in which a new infection occurs, possibly longer than in prevalent cases.

Selection of controls

The selection and comparability of controls are important criteria for ensuring the validity of the case-control study. Order to provide comparable exposure assumptions can be made, the cases and controls of the same base population should belong. The best way to ensure comparability, the selection of controls using the population approach. The controls are taken from a random sample, while the same population as the cases belong. The selection can be made for example by random numbers of the same region. Also good are comparable cases and controls from a cohort. In this case, the study is called nested case -control study. Overall, cases and controls should have the same inclusion criteria as, for example, region or age.

Another way to generate controls that provide hospital controls and controls from the hospital catchment area dar. When choosing, make sure that the controls have no diseases that are associated with the exposure or the disease of interest. However, this type of control is susceptible to interference than the sample of the population.

In order to prevent the cases and controls in characteristics and exposures show differences that really are not in the focus of the investigation, the participants are connected with respect to characteristics such as age, gender, cultural background, socio - economic status and occupation. So that each case is gematscht to a control. This procedure is called in the epidemiology matching.

Difficulties of case -control studies

The main difficulty in case -control studies are the limits of memory ( Recalls ) of the study participants. Because in order to obtain information about the exposures that people are interviewed in retrospect. The most common form is called recall bias. The people may have forgotten a possible exposure, because affected individuals often intense contact with possible causes of the disease apart, which show no correlation for the controls or were forgotten. Thus, the ability to remember different between cases and controls lead to possible misinterpretation.

Assessment

Case-control studies are a relatively inexpensive and often used form of epidemiological studies that can be carried out by small groups or individual researchers in different research institutions, as would often not possible for more structured investigations. They have several important discoveries and advances led the way, but just has their success led to them was met with too much confidence and credibility thereby suffered harm. This is due in large part to incorrect assumptions of such studies.

For case -control studies

A major achievement was the case -control study granted, as Sir Richard Doll and others were able to demonstrate a relationship between tobacco smoking and lung cancer after him. Doll was able to demonstrate a statistically significant association between smoking and lung cancer in a large case-control study. Had skeptics, mostly with support from the tobacco industry for many years ( correctly ) argues that this type of study, no cause / effect chain prove ( causality), but in the end confirmed results of double-blind longitudinal studies the causal relationship that the case-control studies laid close, and it is now widely accepted that tobacco smoking causes about 87 % of all lung cancer -related death in the United States.