
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21742.64    174.1248    22889.96    21401.34    22083.94
experime |  17,281     21905.6    172.1233    22626.85    21568.22    22242.98
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -162.9612    244.8384               -642.8525    316.9301
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    diff = mean(control) - mean(experime)                         t =  -0.6656
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2528         Pr(|T| > |t|) = 0.5057          Pr(T > t) = 0.7472
