
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21707.39     171.369    22527.69    21371.49     22043.3
experime |  17,281    21940.85    174.8648    22987.25    21598.09     22283.6
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            -233.452    244.8368                 -713.34    246.4361
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    diff = mean(control) - mean(experime)                         t =  -0.9535
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.1702         Pr(|T| > |t|) = 0.3403          Pr(T > t) = 0.8298
