
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21742.08    174.1806     22897.3    21400.67    22083.49
experime |  17,281    21906.16    172.0667    22619.41    21568.89    22243.43
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -164.0774    244.8384               -643.9686    315.8139
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    diff = mean(control) - mean(experime)                         t =  -0.6701
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2514         Pr(|T| > |t|) = 0.5028          Pr(T > t) = 0.7486
