 linear models, also depends on the other variable in the interaction (skin thickness). To really understand what is going on, we need to graph the data. Let’s look at the perspective plot like the one we drew for the OLS model, above:</p>
<div class="sourceCode"><pre class="sourceCode r"><code class="sourceCode r"><span class="kw">persp</span>(g1, <span class="dt">theta =</span> <span class="kw">c</span>(<span class="dv">45</span>, <span class="dv">135</span>, <span class="dv">225</span>, <span class="dv