
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21719.67     170.721    22442.51    21385.04     22054.3
experime |  17,281    21928.57    175.4985    23070.54    21584.58    22272.57
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -208.9016    244.8374               -688.7909    270.9878
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    diff = mean(control) - mean(experime)                         t =  -0.8532
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.1968         Pr(|T| > |t|) = 0.3935          Pr(T > t) = 0.8032
