Balanced factorial orthogonality
= Balanced factorial orthogonality
In a complete two-factor design with equal cell replication, centred factor indicator columns for different factors have zero cross-products. Consequently the two main effects in an additive <normal linear model> are <orthogonal>, and their extra sums of squares do not depend on the order in which these main effects are entered. An omitted <interaction term> can still require a separate adequacy check.