
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21813.56     173.232    22772.59    21474.01    22153.11
experime |  17,281    21834.68     173.024    22745.25    21495.54    22173.83
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -21.12488      244.84               -501.0192    458.7695
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    diff = mean(control) - mean(experime)                         t =  -0.0863
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.4656         Pr(|T| > |t|) = 0.9312          Pr(T > t) = 0.5344
