
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21697.21    171.6458    22564.08    21360.77    22033.65
experime |  17,281    21951.03    174.5924    22951.43    21608.81    22293.25
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -253.8187    244.8362               -733.7057    226.0682
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    diff = mean(control) - mean(experime)                         t =  -1.0367
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.1499         Pr(|T| > |t|) = 0.2999          Pr(T > t) = 0.8501
