
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21700.05    172.4478    22669.51    21362.04    22038.07
experime |  17,281    21948.19    173.8005    22847.33    21607.52    22288.85
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -248.1331    244.8364               -728.0203    231.7542
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    diff = mean(control) - mean(experime)                         t =  -1.0135
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.1554         Pr(|T| > |t|) = 0.3108          Pr(T > t) = 0.8446
