99    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"># same but inverting the difference</span></span></span>
<span class="r-in"><span><span class="fu">did_means</span><span class="op">(</span><span class="va">y</span><span clas