
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21722.82    171.8866    22595.74     21385.9    22059.73
experime |  17,281    21925.42    174.3572    22920.51    21583.67    22267.18
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -202.6076    244.8376               -682.4972    277.2821
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    diff = mean(control) - mean(experime)                         t =  -0.8275
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2040         Pr(|T| > |t|) = 0.4079          Pr(T > t) = 0.7960
