
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21766.73    171.5679    22553.84    21430.44    22103.03
experime |  17,281    21881.51    174.6731    22962.04    21539.13    22223.88
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -114.7721    244.8392                -594.665    365.1208
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    diff = mean(control) - mean(experime)                         t =  -0.4688
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.3196         Pr(|T| > |t|) = 0.6392          Pr(T > t) = 0.6804
