Critical analysis of case-control studies in cardiovascular research

It is a research in which the participants are selected between individuals who already have the disease (cases) and between individuals who do not have it (controls); in each of these two groups, the number of exposed individuals is verified, to some risk factor. The goal is to check the possible causal association between exposure to risk factors and disease in study. If the factor is associated with the disease, the factor ratio between the cases will be greater than the same proportion between the controls. This type of study has great application for assitutions in that the disease is relatively infrequent and the time elapsed between exposure to risk and evidence of its effect is long. Case-control studies have limited ethical there is no intervention or prospective observation of risk exposures [1-7].


Introduction
It is a research in which the participants are selected between individuals who already have the disease (cases) and between individuals who do not have it (controls); in each of these two groups, the number of exposed individuals is verified, to some risk factor. The goal is to check the possible causal association between exposure to risk factors and disease in study. If the factor is associated with the disease, the factor ratio between the cases will be greater than the same proportion between the controls. This type of study has great application for assitutions in that the disease is relatively infrequent and the time elapsed between exposure to risk and evidence of its effect is long. Case-control studies have limited ethical there is no intervention or prospective observation of risk exposures [1][2][3][4][5][6][7].

Case selection
The location of cases and controls depends on the characteristics of the disease in study. Cases can be identified in hospitals, specialized clinics or health services (eg, cases of heart failure). It is possible to do a population search of cases, such as biomarkers levels [1][2][3][4][5][6][7].

Selection of controls
The search for controls should follow, as a general guideline, the principle if the control would be a case, it would be found where cases are being found. Controls can be recruited in hospitals where cases have been obtained, in the vicinity of cases, in the same schools, among friends and co-workers of the cases, in the general population under probabilistic sample scheme. In any situation there will be advantages and disadvantages, always with possibility of biased results. Controls obtained by suggestion of the cases themselves can be very similar in their behaviors and customs, and if the risk factor studied is related to habits that may be common among friends, will not be detected. The cost and difficulties in obtaining population controls make this approach practice. In the context of infectious diseases, subclinical and clinical forms of the disease can be detected. The strategy to be adopted to select the control group depends on the objective of the study [1][2][3][4][5][6][7].

Case-control population-based
In this type of outline cases and controls are population; cases can be detected through population screening, defined over a period of time. You can use hospitals to identify all possible cases in the study area or a random sample there. Controls are selected through a probabilistic sample of individuals without belonging to the same geographical area as the cases [1][2][3][4][5][6][7].

Nested case-control
This is a design in which cases and controls are selected in the from a predefined cohort, in which some information about exposures an already available. For each case, controls are randomly selected from individuals at risk at the time of the case diagnosis, which pairing by the time-confusing effect. Additional information is collected and analyzed at the time of the selection of incident cases and controls [1][2][3][4][5][6][7].
Case-control studies are based on a group of individuals affected by the disease in study patients, comparing them with another group of individuals who should be at all similar to cases, differing only for not having that disease, the controls ( Figure 1).
Use this checklist can improve the evaluation of case control studies.