
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21759.83    173.8451     22853.2    21419.08    22100.58
experime |  17,281    21888.41    172.4065    22664.08    21550.48    22226.35
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -128.5807     244.839               -608.4732    351.3118
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    diff = mean(control) - mean(experime)                         t =  -0.5252
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2997         Pr(|T| > |t|) = 0.5995          Pr(T > t) = 0.7003
