="op">+</span><span class="va">period</span><span class="op">~</span><span class="va">treat</span>, <span class="va">base_did</span><span class="op">)</span></span></span>
<span class="r-out co"><span class="r-pr">#&gt;</span>           vars    cond: 1      cond: 0 Difference t-stat</span>
<span class="r-out co"><span class="r-pr">#&gt;</span> 1            y    3.3 (6)     0.68 (5)       2.64   7.83</span>
<span class="r-out co"><span class="r-pr">#&gt;</span> 2           x1 0.13 (3.1) -0.066 (2.8)      0.1