</span> <span class="fu"><a href="https://rdrr.io/r/stats/lm.html" class="external-link">lm</a></span><span class="op">(</span><span class="fu"><a href="https://rdrr.io/r/base/cbind.html" class="external-link">cbind</a></span><span class="op">(</span><span class="va">tear</span>, <span class="va">gloss</span>, <span class="va">opacity</span><span class="op">)</span> <span class="op">~</span> <span class="va">rate</span><span class="op">*</span><span class="va">additive</span>, data<span class="op">=</span><