
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21729.72     171.631    22562.14     21393.3    22066.13
experime |  17,281    21918.52    174.6092    22953.65    21576.27    22260.77
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -188.8038    244.8379               -668.6941    291.0864
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    diff = mean(control) - mean(experime)                         t =  -0.7711
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2203         Pr(|T| > |t|) = 0.4406          Pr(T > t) = 0.7797
