Components of Interaction (3 of 3)


As with other comparisons among means, different procedures are used if the comparison is planned than if it is unplanned. There are as many components to an interaction as the interaction has degrees of freedom. In the present example, the interaction has two degrees of freedom.

The remaining component of the interaction is whether the difference between B1 and B2 is different at A1 than it is at A2. This can be expressed as:

(A1B1-A1B2) - (A2B1 - A2B2)

The coefficients for this comparison are:

A1B1:  1
A1B2: -1
A2B1: -1
A2B2:  1
A3B1:  0
A3B2:  0

For the example, this component of interaction is zero.