
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21920.45    174.5482    22945.62    21578.32    22262.58
experime |  17,281    21727.79     171.693    22570.28    21391.26    22064.33
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            192.6561    244.8378                -287.234    672.5462
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    diff = mean(control) - mean(experime)                         t =   0.7869
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.7843         Pr(|T| > |t|) = 0.4314          Pr(T > t) = 0.2157
