Minitab uses the design matrix as the x-values in regression analysis to fit models specified in .
The design matrix contains n rows, where n is the number of observations, and one or more columns for each term in the model. The first column in the matrix is the intercept, and the column contains all 1s. The columns for the other terms in the model are stored in the order you specified in the Regression main dialog box. Categorical predictors are coded using either 1, 0 or -1, 0, 1 coding. One column of codes is created for each factor level except for the reference level. For more information on how the coding scheme for categorical predictors works, go to Coding schemes for categorical predictors.