Fig. 2. The response surface fit of the interaction data from Short et al. 21 for alfentanil and propofol using the Minto model and residual plots. Top left is the response surface, with points plotted as black triangles if they are more than 2 SDs away from the surface , gray filled circles if they are more than 1 SD away, and circles if they are within 1 SD of the surface prediction. The top right shows the surface contour. The bottom shows the standardized residuals.