  -7.83</span>
<span class="r-out co"><span class="r-pr">#&gt;</span> 2           x1 0.13 (3.1) -0.066 (2.8)     -0.199   -1.1</span>
<span class="r-out co"><span class="r-pr">#&gt;</span> 3       period  5.5 (2.9)    5.5 (2.9)          0      0</span>
<span class="r-out co"><span class="r-pr">#&gt;</span> 4 Observations        550          530                  </span>
<span class="r-in"><span></span></span>
<span class="r-in"><span><span class="co"># now treat/control, before/after</span></span></span>
<sp