
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21699.18    173.4344    22799.21    21359.23    22039.13
experime |  17,281    21949.06    172.8159    22717.89    21610.32     22287.8
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -249.8793    244.8363               -729.7664    230.0079
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    diff = mean(control) - mean(experime)                         t =  -1.0206
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.1537         Pr(|T| > |t|) = 0.3075          Pr(T > t) = 0.8463
