
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21820.38    171.4987    22544.74    21484.22    22156.53
experime |  17,281    21827.87    174.7422    22971.12    21485.35    22170.38
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -7.491904      244.84               -487.3863    472.4025
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    diff = mean(control) - mean(experime)                         t =  -0.0306
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.4878         Pr(|T| > |t|) = 0.9756          Pr(T > t) = 0.5122
