
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21597.57    170.4068    22401.21    21263.55    21931.58
experime |  17,281    22050.68    175.7902    23108.89    21706.11    22395.24
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -453.1113    244.8279               -932.9819    26.75929
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    diff = mean(control) - mean(experime)                         t =  -1.8507
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.0321         Pr(|T| > |t|) = 0.0642          Pr(T > t) = 0.9679
