
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21715.28    173.3422    22787.09    21375.51    22055.04
experime |  17,281    21932.97    172.9096    22730.21    21594.05    22271.89
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -217.6892    244.8372               -697.5782    262.1997
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    diff = mean(control) - mean(experime)                         t =  -0.8891
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.1870         Pr(|T| > |t|) = 0.3739          Pr(T > t) = 0.8130
