
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21762.91    172.7599    22710.54    21424.29    22101.54
experime |  17,281    21885.33    173.4941    22807.05    21545.26    22225.39
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -122.4129    244.8391               -602.3055    357.4798
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    diff = mean(control) - mean(experime)                         t =  -0.5000
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.3085         Pr(|T| > |t|) = 0.6171          Pr(T > t) = 0.6915
