
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21766.02    172.6633    22697.84    21427.58    22104.45
experime |  17,281    21882.23    173.5904    22819.71    21541.97    22222.48
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -116.2112    244.8392                -596.104    363.6816
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    diff = mean(control) - mean(experime)                         t =  -0.4746
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.3175         Pr(|T| > |t|) = 0.6350          Pr(T > t) = 0.6825
