
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21740.12    171.8621    22592.52    21403.25    22076.98
experime |  17,281    21908.12    174.3824    22923.82    21566.32    22249.93
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -168.0065    244.8383               -647.8977    311.8846
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    diff = mean(control) - mean(experime)                         t =  -0.6862
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2463         Pr(|T| > |t|) = 0.4926          Pr(T > t) = 0.7537
