
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21700.69    171.1197    22494.92    21365.28     22036.1
experime |  17,281    21947.55    175.1083    23019.25    21604.32    22290.78
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -246.8675    244.8364               -726.7548    233.0199
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    diff = mean(control) - mean(experime)                         t =  -1.0083
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.1567         Pr(|T| > |t|) = 0.3133          Pr(T > t) = 0.8433
