
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281     22024.8    174.9234    22994.94    21681.93    22367.67
experime |  17,281    21623.44    171.3003    22518.66    21287.67    21959.21
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            401.3624    244.8305               -78.51335    881.2381
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    diff = mean(control) - mean(experime)                         t =   1.6393
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.9494         Pr(|T| > |t|) = 0.1011          Pr(T > t) = 0.0506
