
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21881.04    174.3546    22920.18    21539.29    22222.79
experime |  17,281     21767.2    171.8916    22596.39    21430.28    22104.13
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            113.8379    244.8392                -366.055    593.7308
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    diff = mean(control) - mean(experime)                         t =   0.4649
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.6790         Pr(|T| > |t|) = 0.6420          Pr(T > t) = 0.3210
