an class="r-in"><span><span class="co">## Ex. 2: refitting simulated data using data that contain NA values ------</span></span></span>
<span class="r-in"><span><span class="va">sleepstudyNA</span> <span class="op">&lt;-</span> <span class="va">sleepstudy</span></span></span>
<span class="r-in"><span><span class="va">sleepstudyNA</span><span class="op">$</span><span class="va">Reaction</span><span class="op">[</span><span class="fl">1</span><span class="op">:</span><span class="fl">3</span><span class="op">