
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21748.53     171.861    22592.37    21411.66    22085.39
experime |  17,281    21899.71     174.384    22924.03     21557.9    22241.52
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -151.1874    244.8387               -631.0792    328.7043
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    diff = mean(control) - mean(experime)                         t =  -0.6175
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2685         Pr(|T| > |t|) = 0.5369          Pr(T > t) = 0.7315
