
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21811.91    171.4887    22543.42    21475.77    22148.04
experime |  17,281    21836.33    174.7519     22972.4     21493.8    22178.86
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -24.42472      244.84                -504.319    455.4696
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    diff = mean(control) - mean(experime)                         t =  -0.0998
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.4603         Pr(|T| > |t|) = 0.9205          Pr(T > t) = 0.5397
