
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281     21747.4    172.0046    22611.24    21410.26    22084.55
experime |  17,281    21900.84    174.2423    22905.41     21559.3    22242.37
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            -153.432    244.8386               -633.3237    326.4596
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    diff = mean(control) - mean(experime)                         t =  -0.6267
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2654         Pr(|T| > |t|) = 0.5309          Pr(T > t) = 0.7346
