
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21757.31     171.311    22520.07    21421.53     22093.1
experime |  17,281    21890.93    174.9247    22995.11    21548.06     22233.8
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -133.6124    244.8389               -613.5048    346.2799
------------------------------------------------------------------------------
    diff = mean(control) - mean(experime)                         t =  -0.5457
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2926         Pr(|T| > |t|) = 0.5853          Pr(T > t) = 0.7074
