
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21748.22    172.6932    22701.76    21409.72    22086.71
experime |  17,281    21900.03    173.5599     22815.7    21559.83    22240.22
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -151.8107    244.8386               -631.7025     328.081
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    diff = mean(control) - mean(experime)                         t =  -0.6200
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2676         Pr(|T| > |t|) = 0.5352          Pr(T > t) = 0.7324
