
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21778.47    172.5121    22677.96    21440.33    22116.61
experime |  17,281    21869.77    173.7411    22839.52    21529.22    22210.32
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -91.30163    244.8395               -571.1951    388.5918
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    diff = mean(control) - mean(experime)                         t =  -0.3729
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.3546         Pr(|T| > |t|) = 0.7092          Pr(T > t) = 0.6454
