Coding ordinal independent variables in multiple regression analyses.

The authors present a coding scheme for ordinal independent variables which may be used in various forms of regression analysis. The scheme is useful in dose-response analyses, when the objective is to identify contrasts in the dependent (or response) variable between successive levels of the independent variable, or to identify critical threshold values of the independent variables at which significant changes occur in the response. An example is given of evaluating the survival of lung cancer patients according to their stage of symptomatology. The authors discuss the interpretation of the regression coefficients when this coding scheme is used with linear regression, logistic regression, or in the proportional hazards regression model.