
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21814.29    173.5327    22812.12    21474.14    22154.43
experime |  17,281    21833.96    172.7224     22705.6     21495.4    22172.51
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -19.66971      244.84               -499.5641    460.2246
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    diff = mean(control) - mean(experime)                         t =  -0.0803
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.4680         Pr(|T| > |t|) = 0.9360          Pr(T > t) = 0.5320
