Components of Interaction (3 of 3)

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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.

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