s</a></span>(x, <span class="dt">at =</span> <span class="kw">list</span>(<span class="dt">wt =</span> <span class="kw">fivenum</span>(mtcars<span class="op">$</span>wt)))</code></pre></div>
<pre><code>## Average marginal effects at specified values</code></pre>
<pre><code>## lm(formula = mpg ~ wt + I(wt^2), data = mtcars)</code></pre>
<pre><code>##  at(wt)      wt
##   1.513 -9.8366
##   2.542 -7.4254
##   3.325 -5.5926
##   3.650 -4.8314
##   5.424 -0.6764</code></pre>
<p>The marginal effects in the first