/* Example of using marginscontplot2 for graphical comparison of margins for two diffeent models, linear and quadratic. Patrick Royston, 04jan2018. */ sysuse auto, clear * Define (e.g.) 20 equally spaced plotting values of predictor weight quietly summarize weight range w1 r(min) r(max) 20 * Fit model linear in weight and save margins to file flin.dta. regress mpg weight i.foreign marginscontplot2 weight, var1(w1) ci saving(flin,replace) prefix(lin) * Fit model quadratic in weight and save margins to file fquad.dta. gen w2 = weight^2 regress mpg weight w2 i.foreign gen w1a = w1 gen w1b = w1^2 marginscontplot2 weight (weight w2), var1(w1 (w1a w1b)) ci saving(fquad,replace) prefix(quad) use fquad, clear lab var quad_margin "Quadratic" save fquad,replace use flin, clear lab var lin_margin "Linear" save flin,replace * Merge files and plot margins against "weight" merge 1:1 _n using fquad line lin_margin quad_margin weight * Note: Could include pointwise confidence intervals in plot if desired.