
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21850.97    174.0123    22875.17    21509.88    22192.05
experime |  17,281    21797.28     172.239    22642.06    21459.67    22134.88
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            53.69012    244.8398               -426.2039    533.5842
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    diff = mean(control) - mean(experime)                         t =   0.2193
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.5868         Pr(|T| > |t|) = 0.8264          Pr(T > t) = 0.4132
