
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21607.44    170.2303       22378    21273.77    21941.11
experime |  17,281     22040.8    175.9626    23131.56     21695.9    22385.71
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            -433.363    244.8289               -913.2356    46.50966
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    diff = mean(control) - mean(experime)                         t =  -1.7701
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.0384         Pr(|T| > |t|) = 0.0767          Pr(T > t) = 0.9616
