
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21721.82    171.6633    22566.37    21385.34     22058.3
experime |  17,281    21926.42     174.577    22949.41    21584.23    22268.61
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -204.5984    244.8375                -684.488    275.2911
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    diff = mean(control) - mean(experime)                         t =  -0.8356
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2017         Pr(|T| > |t|) = 0.4034          Pr(T > t) = 0.7983
