
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21717.32    173.4915    22806.71    21377.25    22057.38
experime |  17,281    21930.93      172.76    22710.55     21592.3    22269.55
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -213.6113    244.8373               -693.5004    266.2778
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    diff = mean(control) - mean(experime)                         t =  -0.8725
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.1915         Pr(|T| > |t|) = 0.3830          Pr(T > t) = 0.8085
