Epidemiological studies about contagious diseases have two very specific characteristics. The first refers to the object, which is only a source of damage. The second relates to the goals, which aim to determine the relationship between cause and effect, ., between exposure and disease. So, even with multifactorial determinants, it's an unidimensional evaluation. Therefore, in a evaluation between exposed and unexposed, the concept of risk approaches the definition of probability. However, when the objective includes the judgment about the severity of the injury or the comparison of different injuries in different exposures, the probability becomes one of the information that compose the concept of risk
