<span class="va">sex</span> <span class="op">&lt;-</span> <span class="fu"><a href="https://rdrr.io/r/base/factor.html" class="external-link">factor</a></span><span class="op">(</span><span class="va">sex</span>, levels <span class="op">=</span> <span class="fu"><a href="https://rdrr.io/r/base/c.html" class="external-link">c</a></span><span class="op">(</span><span class="st">"Male"</span>, <span class="st">"Female"</span><span class="op">)</span>, labels <span class="op">=</span> <span class="fu"><a href="