
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21745.68    172.7791    22713.06    21407.01    22084.34
experime |  17,281    21902.57    173.4742    22804.43    21562.54    22242.59
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -156.8904    244.8385                -636.782    323.0011
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    diff = mean(control) - mean(experime)                         t =  -0.6408
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2608         Pr(|T| > |t|) = 0.5217          Pr(T > t) = 0.7392
