Then, we fit the mean-centered version of this equation, Equation 12, to the data (see middle section Table 1). The mean-centered equation gave the same estimate of the interaction effect and an identical estimate of cross-over point, Ĉ = (−(1.56)/17.51)+2.83 = 2.74, using Equation 6, as with raw-scored predictors. Thus, both raw-scored and mean-centered equations provided evidence that the interaction was disordinal, with a point estimate of C close to the sample mean on X1, although lack of a SE for the cross-over point hinders full interpretation.
