
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21811.46    171.6887    22569.71    21474.94    22147.99
experime |  17,281    21836.78    174.5555    22946.58    21494.63    22178.92
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -25.31303      244.84               -505.2073    454.5813
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    diff = mean(control) - mean(experime)                         t =  -0.1034
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.4588         Pr(|T| > |t|) = 0.9177          Pr(T > t) = 0.5412
