op">*</span>dummyZ))</a>
<a class="sourceLine" id="cb1-10" data-line-number="10">dat &lt;-<span class="st"> </span><span class="kw">as.data.frame</span>(<span class="kw">cbind</span>(Y, X, W, Z))</a>
<a class="sourceLine" id="cb1-11" data-line-number="11">dat<span class="op">$</span>X &lt;-<span class="st"> </span><span class="kw">as.numeric</span>(dat<span class="op">$</span>X); dat<span class="op">$</span>X &lt;-<span class="st"> </span><span class="kw">ifelse</span>(dat<span class="op">$</span>X <span cl