
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21846.32    172.6646       22698    21507.88    22184.76
experime |  17,281    21801.92    173.5901    22819.67    21461.67    22142.18
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            44.39911    244.8399               -435.4951    524.2933
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    diff = mean(control) - mean(experime)                         t =   0.1813
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.5719         Pr(|T| > |t|) = 0.8561          Pr(T > t) = 0.4281
