> parameter is needed to retain <code>NA</code> values in the model frame that <code><a href="../reference/hlm_resid.default.html">hlm_resid()</a></code> returns. To demonstrate this requirement, we create a duplicate data set of <code>Exam</code> with the standardized LRT scores set to <code>NA</code> for observations 1, 2, and 5.</p>
<div class="sourceCode" id="cb7"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span class="co"># make copy of Exam data set</span>
<span class="va">Exam2</sp