 understand the marginal effect of each variable. For example, we might want to look at the effects of each variable for vehicles with varying axle ratios but also across some representative values of the <code>wt</code> distribution, separately for manual and automatic vehicles. (Note that the order of values in the <code>at</code> object does matter and it can inclue variables that are not explicitly being modelled).</p>
<div class="sourceCode"><pre class="sourceCode r"><code class="sourceCode r">wts &lt;