Product of Columns

To add column(s) to the design matrix consisting of the product(s) of existing columns, select the FillCol, Product of Columns choices. Columns are added to the right side of the matrix, and filled with the products of columns you specify. You are asked for the first block of columns, e.g., 2 through 5, and then for a second block of columns, e.g., 6 through 7. You can specify a single column for either block (or both blocks) by giving a single column, e.g. 3 through 3. This command is useful for building interaction terms in the design matrix. As an example, suppose the following design matrix is on the screen.

Suppose you specify that the first block of columns is 1 through 1, and the second block of columns is 2 through 3. The resulting matrix would look like this.