ABSTRACT
An understanding of the concept of risk is fundamental to an understanding of the subsequent chapters on prognosis, treatment, and cause. Risk factors for many animal diseases are poorly defined or unknown and only come to light through the systematic study of naturally or spontaneously occurring cases. Univariate analysis is the simplest approach to exploring the association between a potential risk factor and an outcome of interest. Cross-sectional studies are especially useful for testing the possible causal association between a number of potential risk factors, or variables, and an outcome of interest. Multivariate, or multivariable, logistic regression is used to assess the contribution of each of a number of potential risk factors to a dichotomous outcome, such as disease or death, while controlling for confounding. Relative risk, or risk ratio, is calculated by dividing incidence in individuals exposed to a risk factor by incidence in nonexposed individuals.
