
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21804.52    174.9817    23002.61    21461.54    22147.51
experime |  17,281    21843.72    171.2541    22512.59    21508.04    22179.39
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            -39.1939    244.8399               -519.0881    440.7003
------------------------------------------------------------------------------
    diff = mean(control) - mean(experime)                         t =  -0.1601
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.4364         Pr(|T| > |t|) = 0.8728          Pr(T > t) = 0.5636
