
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21743.05    173.0633    22750.42    21403.83    22082.27
experime |  17,281    21905.19    173.1906    22767.15    21565.72    22244.66
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -162.1439    244.8385               -642.0352    317.7475
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    diff = mean(control) - mean(experime)                         t =  -0.6622
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2539         Pr(|T| > |t|) = 0.5078          Pr(T > t) = 0.7461
