
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21979.58    173.7542    22841.24       21639    22320.15
experime |  17,281    21668.67    172.4915    22675.25    21330.56    22006.77
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            310.9106    244.8343               -168.9726    790.7938
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    diff = mean(control) - mean(experime)                         t =   1.2699
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.8979         Pr(|T| > |t|) = 0.2041          Pr(T > t) = 0.1021
