
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21742.61    173.5741    22817.57    21402.39    22082.83
experime |  17,281    21905.63    172.6786    22699.84    21567.16     22244.1
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |             -163.02    244.8384               -642.9113    316.8714
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    diff = mean(control) - mean(experime)                         t =  -0.6658
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2528         Pr(|T| > |t|) = 0.5055          Pr(T > t) = 0.7472
