
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21902.45    173.3843    22792.62     21562.6     22242.3
experime |  17,281     21745.8    172.8693    22724.92    21406.95    22084.64
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            156.6507    244.8386               -323.2408    636.5423
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    diff = mean(control) - mean(experime)                         t =   0.6398
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.7389         Pr(|T| > |t|) = 0.5223          Pr(T > t) = 0.2611
