<span class="kw">c</span>(<span class="st">&quot;ID&quot;</span>, <span class="st">&quot;gender&quot;</span>, <span class="st">&quot;age&quot;</span>, <span class="kw">paste0</span>(<span class="st">&quot;phq&quot;</span>, <span class="dv">1</span><span class="op">:</span><span class="dv">9</span>))]

<span class="co"># turn gender into a proper factor ---------------------------</span>
t0<span class="op">$</span>gender &lt;-<span class="st"> </span><span class="kw">factor</span>(t0<span class="op">$</span>