
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21735.26    171.1022    22492.62    21399.88    22070.63
experime |  17,281    21912.99    175.1278    23021.82    21569.72    22256.25
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -177.7292    244.8381                 -657.62    302.1615
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    diff = mean(control) - mean(experime)                         t =  -0.7259
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2340         Pr(|T| > |t|) = 0.4679          Pr(T > t) = 0.7660
