n> <span class="op">~</span> <span class="va">NegPerChick</span><span class="op">|</span> <span class="va">FoodTreatment</span><span class="op">:</span><span class="va">SexParent</span>,</span></span>
<span class="r-in"><span>        data<span class="op">=</span><span class="va">Owls</span><span class="op">)</span></span></span>
<span class="r-plt img"><img src="Owls-2.png" alt="" width="700" height="433"></span>
<span class="r-in"><span><span class="kw">if</span> <span class="op">(</span><span class="cn">F