Random graphs (18): Simple interaction plots with -marginsplot- for categorical and continuous variables

sysuse auto, clear

reg mpg c.weight##i.foreign

qui sum weight

local minsd = r(mean) - r(sd)
local mean  = r(mean)
local plusd = r(mean) + r(sd)

margins foreign, at(weight = (`minsd' `mean' `plusd'))

marginsplot, recast(line) noci scheme(lean1) ///
             name(first, replace)
gr export first.png, as(png) replace
// Impossible to tell the difference between
// domestic and foreign lines because of the lean scheme

marginsplot, recast(line) noci ///
             plot1opts(lpattern(dash)) ///
             scheme(lean1) ///
             name(second, replace)
gr export second.png, as(png) replace
// That fixes the problem

marginsplot, recast(line) recastci(rarea) ciopts(color(gs10)) ///
             plot1opts(lpattern(dash)) ///
             scheme(lean1) ///
             name(third, replace)
gr export third.png, as(png) replace
// That's a nice way of plotting CI's

marginsplot, recast(line) recastci(rarea) ciopts(color(gs10)) ///
             plot1opts(lpattern(dash)) ///
             ytitle("Predicted mileage") ///
             title("Car type moderates the weight{char 0150}mileage association") ///
             xlabel(`minsd' "-1 SD" `mean' "Average weight (lbs.)" `plusd' "+1 SD") ///
             xtitle("") ///
             scheme(lean1) ///
             name(fourth, replace)
gr export fourth.png, as(png) replace
// That labels the graph nicely