
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21813.19     173.393    22793.76    21473.32    22153.05
experime |  17,281    21835.06    172.8626    22724.04    21496.23    22173.89
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -21.87162      244.84                -501.766    458.0227
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    diff = mean(control) - mean(experime)                         t =  -0.0893
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.4644         Pr(|T| > |t|) = 0.9288          Pr(T > t) = 0.5356
