de></pre>
<pre><code>## lm(formula = mpg ~ cyl + wt + hp * am, data = mtcars)</code></pre>
<pre><code>##  at(am)     cyl     wt        hp    am
##       0 -0.9339 -2.812 -0.008945 1.034
##       1 -0.9339 -2.812 -0.026392 1.034</code></pre>
<p>Because of the <code>hp * am</code> interaction in the regression, the marginal effect of horsepower differs between the two sets of results. We can also specify more than one variable to <code>at</code>, creating a potentially long list of marginal effects results. F