
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21733.27    170.3379    22392.15    21399.39    22067.15
experime |  17,281    21914.98    175.8712    23119.53    21570.25     22259.7
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -181.7097    244.8381               -661.6003    298.1809
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    diff = mean(control) - mean(experime)                         t =  -0.7422
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2290         Pr(|T| > |t|) = 0.4580          Pr(T > t) = 0.7710
