The tests of the fixed effect terms are F tests. The null hypothesis for the test depends on whether the test is for a fixed factor term or a covariate term. For a fixed factor term, the null hypothesis is that the term does not significantly affect the response. For a covariate term, the null hypothesis is that no association exists between the response and the covariate term.
Minitab offers 2 methods to test fixed effect terms: Kenward-Roger approximation and Satterthwaite approximation. For more information on Kenward-Roger approximation, see Kenward and Roger.1 For more information on Satterthwaite approximation, see Giesbrecht and Burns 2 as well as Fai and Cornelius. 3
The calculation of the denominator degrees of freedom for the F-statistic and the calculation of the F-statistic differ. The calculation of the numerator degrees of freedom and the determination of a p-value for a given F-statistic are the same for both methods.