Using "regress chronicity age" as an example:
The total variance has N-1 degrees of freedom. In this case, there were N=401 study participants, so the total DF for is 400.
The model degrees of freedom corresponds to the number of predictors + the intercept minus 1 (K-1). Including the intercept, there are 2 predictors, so the model has 2-1=1 degrees of freedom.
The residual degrees of freedom is the DF total minus the DF model, 400 – 1 is 399.
**When displaying the exact p-value using the ttail function you would use the total DF (400) - NOT - the model DF (1) like I mistakingly did during lecture yesterday.