
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21724.85    171.1764    22502.37    21389.33    22060.37
experime |  17,281    21923.39    175.0546     23012.2    21580.27    22266.52
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -198.5455    244.8377               -678.4354    281.3443
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    diff = mean(control) - mean(experime)                         t =  -0.8109
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2087         Pr(|T| > |t|) = 0.4174          Pr(T > t) = 0.7913
