
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21723.51    172.7958    22715.26    21384.81    22062.21
experime |  17,281    21924.73    173.4562    22802.07    21584.74    22264.72
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -201.2238    244.8376               -681.1135    278.6659
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    diff = mean(control) - mean(experime)                         t =  -0.8219
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2056         Pr(|T| > |t|) = 0.4112          Pr(T > t) = 0.7944
