
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21792.61    171.8858    22595.63     21455.7    22129.53
experime |  17,281    21855.63     174.361    22921.02    21513.86    22197.39
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -63.01353    244.8398               -542.9075    416.8804
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    diff = mean(control) - mean(experime)                         t =  -0.2574
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.3984         Pr(|T| > |t|) = 0.7969          Pr(T > t) = 0.6016
