
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21715.18    171.9551    22604.74    21378.13    22052.23
experime |  17,281    21933.06    174.2891    22911.56    21591.43    22274.68
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -217.8731    244.8372                -697.762    262.0158
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    diff = mean(control) - mean(experime)                         t =  -0.8899
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.1868         Pr(|T| > |t|) = 0.3735          Pr(T > t) = 0.8132
