
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21945.08    175.8609    23118.19    21600.37    22289.78
experime |  17,281    21703.17    170.3463    22393.25    21369.27    22037.06
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            241.9093    244.8365               -237.9783    721.7969
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    diff = mean(control) - mean(experime)                         t =   0.9880
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.8384         Pr(|T| > |t|) = 0.3231          Pr(T > t) = 0.1616
