
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21755.78    173.7709    22843.44    21415.17    22096.39
experime |  17,281    21892.46    172.4812     22673.9    21554.38    22230.54
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -136.6781    244.8389               -616.5704    343.2141
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    diff = mean(control) - mean(experime)                         t =  -0.5582
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2883         Pr(|T| > |t|) = 0.5767          Pr(T > t) = 0.7117
