
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21762.44     172.087    22622.08    21425.13    22099.75
experime |  17,281     21885.8    174.1615    22894.79    21544.43    22227.18
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -123.3601    244.8391               -603.2527    356.5326
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    diff = mean(control) - mean(experime)                         t =  -0.5038
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.3072         Pr(|T| > |t|) = 0.6144          Pr(T > t) = 0.6928
