
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21764.82     173.594    22820.18    21424.56    22105.08
experime |  17,281    21883.42    172.6596    22697.35    21544.99    22221.85
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -118.6052    244.8392                -598.498    361.2876
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    diff = mean(control) - mean(experime)                         t =  -0.4844
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.3140         Pr(|T| > |t|) = 0.6281          Pr(T > t) = 0.6860
