
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21755.01    173.5374    22812.74    21414.86    22095.16
experime |  17,281    21893.23    172.7161    22704.78    21554.69    22231.77
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -138.2143    244.8389               -618.1065    341.6779
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    diff = mean(control) - mean(experime)                         t =  -0.5645
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2862         Pr(|T| > |t|) = 0.5724          Pr(T > t) = 0.7138
