
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21713.77    171.7562    22578.59    21377.11    22050.43
experime |  17,281    21934.47    174.4851    22937.32    21592.47    22276.48
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -220.7057    244.8371               -700.5944    259.1831
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    diff = mean(control) - mean(experime)                         t =  -0.9014
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.1837         Pr(|T| > |t|) = 0.3674          Pr(T > t) = 0.8163
