Conceptos básicos sobre metodología bioestadística: Aclaración sobre los términos proporciones, frecuencias relativas, porcentajes y riesgos relativos

Abstract

In medical research, it is very common to report results in terms of proportions and relative risks (RR). Unfortunately, the researchers do not always interpret these figures correctly and, sometimes, the media publish erroneous information. By these reasons, in this article we used several examples to explain different concepts, and the real meaning when the value of a relative risk is expressed in form of percentage. If we say that the exposition to a certain factor (let say smoking) increases the probability of getting a certain disease (i.e. lung cancer) in a 90%, the interpretation is frequently erroneous. What we are saying is that individuals exposed to tobacco have a risk of getting the disease (lung cancer) 1,9 times greater than those individuals not exposed to tobacco (Relative Risk = 1,9). That is, that the exposition to the study factor (tobacco) almost doubles the chances of getting the disease. Similarly, if we would like to express a relative risk of 4 in percentage, this should be expressed saying that the exposure to tobacco increases the probability to develop lung cancer of 400%.