Hi, For this type of question, how do we count the degrees of freedom? (ie. Why is the degrees of freedom 12 for the null model?)
The important thing is the difference in the number of degrees of freedom. This is the same as the difference in the number of parameters when comparing two nested models. The models in this question have 1, 3, 6 and 12 parameters respectively. So the differences are 2, 3 and 6. The examiners didn't specify the number of observations used when fitting the models, so we cannot work out the df for each model.
