Either a t-test or F-test can be used.

For an F-test, the contrast should contain a 1 for the interaction column and zeros elsewhere.

For a t-test, the contrast should contain a 1 or -1 for the interaction column and zeros elsewhere.

A t-test will allow you to test for positive and negative interactions separately.

F-test is sensitive to any kind of interaction (positive or negative).


Originally posted by Ana Coelho: