
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21744.44    170.7475       22446    21409.76    22079.13
experime |  17,281     21903.8    175.4741    23067.34    21559.85    22247.74
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            -159.353    244.8385               -639.2444    320.5385
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    diff = mean(control) - mean(experime)                         t =  -0.6508
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2576         Pr(|T| > |t|) = 0.5151          Pr(T > t) = 0.7424
