
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21768.18    172.4557    22670.55    21430.15    22106.21
experime |  17,281    21880.06    173.7967    22846.83     21539.4    22220.72
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -111.8834    244.8393               -591.7763    368.0096
------------------------------------------------------------------------------
    diff = mean(control) - mean(experime)                         t =  -0.4570
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.3238         Pr(|T| > |t|) = 0.6477          Pr(T > t) = 0.6762
