Introduction to the study of clinical investigation bias

Abstract

Science is a powerful ally in the search for the answers to some of the most important medical questions, suchas the cause of diseases or the effects of drugs or therapeutical procedures. The scientific method, which consists in an ordered set of predefined steps, confers a high level of validity to the knowledge acquired by its use. In this way, clinical scientific studies that employ it can produce valid knowledge about the causes of diseases or the effect of treatment procedures. Althoughthe nature of causal relationship is a matter of intense debate, in medicine it is usually sufficient to consider that a causal relationship exists when there is no better explanation for an observed association (i.e. when the rate of the studied event is higher in the group ofsubjects exposed to the risk factor studied as compared to subjects that were not exposed). The term “a betterexplanation” usually refers to bias, which generically refers to a set of factors whose occurrence greatly reduces the credibility or the generalizability of the clinicalstudy results. These factors can occur during the selection of the subjects to be studied or during the conductionof the study. Selection bias occurs when the characteristics of the exposed and unexposed subjects differ, making it impossible to rule out the possibilitythat any difference in the event rate observed is due to these differences and not the risk factor. On the otherhand, Information bias occurs when exposed and unexposed subjects are not evaluated similarly during the study, which can raise doubt in the case that a difference in the occurrence of the event is observed.