
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21790.68    172.7081    22703.73    21452.16    22129.21
experime |  17,281    21857.56    173.5465    22813.94    21517.39    22197.73
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -66.87788    244.8397               -546.7718     413.016
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    diff = mean(control) - mean(experime)                         t =  -0.2731
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.3924         Pr(|T| > |t|) = 0.7847          Pr(T > t) = 0.6076
