
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21713.64    171.9048    22598.12    21376.69    22050.59
experime |  17,281     21934.6    174.3387    22918.08    21592.88    22276.32
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -220.9634    244.8371               -700.8521    258.9254
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    diff = mean(control) - mean(experime)                         t =  -0.9025
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.1834         Pr(|T| > |t|) = 0.3668          Pr(T > t) = 0.8 166
