
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21749.58    175.2478    23037.59    21406.08    22093.08
experime |  17,281    21898.66    170.9801    22476.57    21563.52     22233.8
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            -149.083    244.8387               -628.9748    330.8088
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    diff = mean(control) - mean(experime)                         t =  -0.6089
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2713         Pr(|T| > |t|) = 0.5426          Pr(T > t) = 0.7287
