
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21669.16    173.1127    22756.91    21329.84    22008.48
experime |  17,281    21979.08    173.1353    22759.89    21639.72    22318.44
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -309.9204    244.8343               -789.8037    169.9629
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    diff = mean(control) - mean(experime)                         t =  -1.2658
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.1028         Pr(|T| > |t|) = 0.2056          Pr(T > t) = 0.8972
