The degrees of freedom in a multiple regression equals N−k−1, where k is the number of variables. Does k include dummy variables?
For example, I have the model: Y=B1+B2D2+B3D3+B4D4+B5X1+B6X2+B7(D2D3)+B9(D2D4)+B9(D3D4)+B10(D2D3D4)+u (there are 2 X variables and 3 dummies)
N=14780 To get the Degrees of Freedom would i use 14780-2-1 or 14780-5-1 or something else entirely?