
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21747.28    173.5708    22817.13    21407.06     22087.5
experime |  17,281    21900.96    172.6822    22700.32    21562.49    22239.44
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -153.6818    244.8386               -633.5734    326.2099
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    diff = mean(control) - mean(experime)                         t =  -0.6277
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2651         Pr(|T| > |t|) = 0.5302          Pr(T > t) = 0.7349
