
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.                                             [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21910.96    173.8699    22856.45                                              21570.16                                              22251.76
experime |  17,281    21737.28    172.3804    22660.65                                               21399.4                                              22075.17
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6                                              21584.18                                              22064.06
---------+--------------------------------------------------------------------
    diff |            173.6769    244.8382                -306.214                                              653.5678
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    diff = mean(control) - mean(experime)                         t =   0.7094
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.7609         Pr(|T| > |t|) =  0.4781          Pr(T > t) = 0.2391
