They are only studies that offer to study Measure the exposure and outcome, in the
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Compare exposure and the outcome between Inappropriate use of historic controls lead a Historic controls are used in preliminary Also, they are called historic controls.īeginning Intervention only in subjects Time We compare the results with the results ofĪnother researcher or with the results of a There are clinical trials with external controls. Group and intervention 2 is administrated toīeginning of Intervention Intervention Time Intervention 1 is administrated to control Space (wash out period) without it, then the After, interventions are suspended, and left a There are clinical trials with auto controls. Double blind is when neither subjects nor Blind single is when the subjects do not know By ethics reasons, only it is permitted The allocation of subjects in experimental or Receive the intervention, it is a control group.
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Randomize selected and we do not know what It is administrated an intervention to a group, It is not useful to search causes of the The sample can not be representative from Populations little willing to collaborate. Useful to evaluate diagnostic procedures. They are useful to know the burden of a Describe a disease and its importance for the Analyze data of a subjects group in a point of They are useful when we study two or more They adequate when the exposure is rare.
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To know the natural history of disease. They are adequate to know the causes of an Retrospective (historic), if it go back in the The cohort study can be prospective if theįollow up is forward in the time or it can be We follow up to prove if they develop the The outcome and they are classified if have or Subjects are selected because do not have Control group should be adequately selected,īecause they represent the population without the They depend on the quality of registries. It is not necessary to wait to present outcome. They are adequate to outcomes with long latency They are adequate to study rare outcomes. Cases or report Cases and Cohort Cross sectional Ecologicĭirection of research Beginning of study Time