
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21740.62    171.9712    22606.85    21403.54     22077.7
experime |  17,281    21907.62    174.2749    22909.69    21566.03    22249.22
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -167.0044    244.8384               -646.8956    312.8867
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    diff = mean(control) - mean(experime)                         t =  -0.6821
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2476         Pr(|T| > |t|) = 0.4952          Pr(T > t) = 0.7524
