GRM Introductory Overview - Homogeneity of Slopes
The appropriate design for modeling the influences of continuous and categorical predictor variables depends on whether the continuous and categorical predictors interact in influencing the outcome. The traditional analysis of covariance (ANCOVA) design for continuous and categorical predictor variables is appropriate when the continuous and categorical predictors do not interact in influencing responses on the outcome. The homogeneity of slopes designs can be used to test whether the continuous and categorical predictors interact in influencing responses. For the same example data used to illustrate the traditional ANCOVA design, the sigma-restricted X matrix for the homogeneity of slopes design would be
Using this design matrix X, if the b4 and b5 coefficients in the regression equation
Y = b0 + b1X1 + b2X2 + b3X3 + b4X4 + b5X5
are zero, the simpler traditional ANCOVA design should be used.
Between-Subject Designs
Multivariate designs