ely difficult to convey standard errors or confidence intervals in a three-dimensional plot, so those could be quite valuable.</p>
<p>It is also worth comparing the above graphs to those that would result from a model without the interaction term between <code>age</code> and <code>skin</code>. It looks quite different (note, however, that it is also drawn from a higher perspective to better see the shape of the surface):</p>
<p><img src="Introduction_files/figure-html/unnamed-chunk-39-1.png" width="768"><im