
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21551.82    169.2832     22253.5    21220.01    21883.63
experime |  17,281    22096.42     176.865    23250.18    21749.75     22443.1
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -544.6045    244.8225               -1024.465   -64.74443
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    diff = mean(control) - mean(experime)                         t =  -2.2245
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.0131         Pr(|T| > |t|) = 0.0261          Pr(T > t) = 0.9869
