Multiple regression analysis is a very powerful statistical tool that provides a mathematical model of some physiological situation in life. The model can include simultaneously both quantitative and qualitative factors in the prediction of a continuous response variable. Quantitative factors are generally modeled by using either polynomial, exponential, or logarithmic equations, whereas qualitative factors are modeled by using dummy variables. The researcher must determine the factors to include in the model, their possible interactions, and the appropriate form of the model, and then the least squares theory is used to find the best equation of that form. Other statistical analyses, such as discriminant analysis and log linear models, are available for situations in which the response variable is non-numerical.