
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21724.64    171.2975    22518.29    21388.88     22060.4
experime |  17,281     21923.6    174.9361    22996.62    21580.71    22266.49
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -198.9619    244.8377               -678.8517    280.9279
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    diff = mean(control) - mean(experime)                         t =  -0.8126
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2082         Pr(|T| > |t|) = 0.4164          Pr(T > t) = 0.7918
