
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21811.91    171.9429    22603.14    21474.88    22148.93
experime |  17,281    21836.34     174.305    22913.66    21494.68    22177.99
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -24.42883      244.84               -504.3232    455.4655
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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
