
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281     21545.9    168.4551    22144.64    21215.71    21876.09
experime |  17,281    22102.34    177.6529    23353.75    21754.12    22450.56
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -556.4393    244.8217               -1036.298   -76.58078
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    diff = mean(control) - mean(experime)                         t =  -2.2728
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.0115         Pr(|T| > |t|) = 0.0230          Pr(T > t) = 0.9885
