
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21696.88    171.9498    22604.05    21359.84    22033.92
experime |  17,281    21951.36    174.2929    22912.06    21609.73    22292.99
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            -254.479    244.8362               -734.3659    225.4079
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    diff = mean(control) - mean(experime)                         t =  -1.0394
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.1493         Pr(|T| > |t|) = 0.2986          Pr(T > t) = 0.8507
