
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21624.68    170.9035     22466.5    21289.69    21959.67
experime |  17,281    22023.56    175.3112    23045.92    21679.94    22367.19
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -398.8855    244.8306               -878.7615    80.99043
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    diff = mean(control) - mean(experime)                         t =  -1.6292
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.0516         Pr(|T| > |t|) = 0.1033          Pr(T > t) = 0.9484
