
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21774.25    173.0258     22745.5    21435.11     22113.4
experime |  17,281    21873.99    173.2293    22772.25    21534.44    22213.54
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -99.73503    244.8394               -579.6283    380.1582
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    diff = mean(control) - mean(experime)                         t =  -0.4073
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.3419         Pr(|T| > |t|) = 0.6838          Pr(T > t) = 0.6581
