
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21791.32    172.4475    22669.47     21453.3    22129.33
experime |  17,281    21856.92    173.8056    22847.99    21516.25     22197.6
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -65.60596    244.8397               -545.4999    414.2879
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    diff = mean(control) - mean(experime)                         t =  -0.2680
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.3944         Pr(|T| > |t|) = 0.7887          Pr(T > t) = 0.6056
