
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281     21903.4    175.1453    23024.11     21560.1    22246.71
experime |  17,281    21744.84    171.0849    22490.34    21409.49    22080.18
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            158.5669    244.8385               -321.3246    638.4584
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    diff = mean(control) - mean(experime)                         t =   0.6476
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.7414         Pr(|T| > |t|) = 0.5172          Pr(T > t) = 0.2586
