tercept. </span></span></span>
<span class="r-in"><span><span class="co">#add group variables for 3 level model </span></span></span>
<span class="r-in"><span><span class="va">ss1</span><span class="op">$</span><span class="va">Group</span> <span class="op">&lt;-</span> <span class="fl">3</span></span></span>
<span class="r-in"><span><span class="va">ss1</span><span class="op">$</span><span class="va">Group</span> <span class="op">&lt;-</span> <span class="fu"><a href="https://rdrr.io/r/base/ifelse.html" cl