
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21707.36    170.4984    22413.24    21373.17    22041.56
experime |  17,281    21940.88    175.7138    23098.85    21596.46     22285.3
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -233.5173    244.8368               -713.4054    246.3708
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    diff = mean(control) - mean(experime)                         t =  -0.9538
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.1701         Pr(|T| > |t|) = 0.3402          Pr(T > t) = 0.8 299
