After presenting standard ways of parameterizing regression models with interaction effects, we derived a re-parameterized regression model for linear X linear interaction of two quantitative predictors. The most important benefit of a re-parameterized equation is the SE and associated CI of the estimated cross-over point Ĉ. Further, as stressed throughout, the CI of Ĉ allows a more informed evaluation of the ordinal vs. disordinal form of the interaction.
