
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21572.07    170.1759    22370.85    21238.51    21905.64
experime |  17,281    22076.17    176.0098    23137.76    21731.17    22421.16
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -504.0931     244.825                -983.958   -24.22811
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    diff = mean(control) - mean(experime)                         t =  -2.0590
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.0198         Pr(|T| > |t|) = 0.0395          Pr(T > t) = 0.9802
