
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21758.11    172.8577    22723.39    21419.29    22096.92
experime |  17,281    21890.14    173.3965    22794.22    21550.26    22230.01
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -132.0293     244.839               -611.9217    347.8631
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    diff = mean(control) - mean(experime)                         t =  -0.5392
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2949         Pr(|T| > |t|) = 0.5897          Pr(T > t) = 0.7051
