na.omit</span>(airquality)</a>
<a class="sourceLine" id="cb8-3" data-line-number="3"><span class="co"># define binary ozone level</span></a>
<a class="sourceLine" id="cb8-4" data-line-number="4">ozonedat<span class="op">$</span>ozone1 &lt;-<span class="st"> </span><span class="kw">ifelse</span>(ozonedat<span class="op">$</span>Ozone <span class="op">&lt;</span><span class="st"> </span><span class="kw">quantile</span>(ozonedat<span class="op">$</span>Ozone, <span class="dt">prob =</span> <span class="fl">0.1