
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21727.51    173.0703    22751.34    21388.27    22066.74
experime |  17,281    21920.73    173.1826     22766.1    21581.28    22260.19
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -193.2237    244.8378               -673.1138    286.6664
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    diff = mean(control) - mean(experime)                         t =  -0.7892
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2150         Pr(|T| > |t|) = 0.4300          Pr(T > t) = 0.7850
