
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21623.88    170.3656    22395.78    21289.95    21957.81
experime |  17,281    22024.36    175.8339    23114.64    21679.71    22369.01
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -400.4823    244.8305               -880.3581    79.39352
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    diff = mean(control) - mean(experime)                         t =  -1.6358
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.0510         Pr(|T| > |t|) = 0.1019          Pr(T > t) = 0.9490
