
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21709.43    172.8179    22718.16    21370.69    22048.17
experime |  17,281    21938.81    173.4332    22799.05    21598.86    22278.76
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -229.3761    244.8369               -709.2644    250.5122
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    diff = mean(control) - mean(experime)                         t =  -0.9369
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.1744         Pr(|T| > |t|) = 0.3488          Pr(T > t) = 0.8256
