Error Degrees of Freedom are calculated as n - p - 1 for multiple regression models. The p represents the number of coefficients (not including the intercept) in the estimated model.

Report the Error Degrees of Freedom for this example:

Assume 166 observations are used to estimate a model with 2 numerical explanatory variables both with a linear relationship to the response and 1 categorical explanatory variable. The categorical variable has 4 levels.