
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21753.49    172.5256    22679.74    21415.33    22091.66
experime |  17,281    21894.75    173.7267    22837.63    21554.23    22235.27
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            -141.255    244.8388               -621.1471    338.6371
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    diff = mean(control) - mean(experime)                         t =  -0.5769
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2820         Pr(|T| > |t|) = 0.5640          Pr(T > t) = 0.7180
