
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21544.57    169.6562    22302.53    21212.02    21877.11
experime |  17,281    22103.68     176.506    23202.98    21757.71    22449.65
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -559.1092    244.8215               -1038.967   -79.25098
------------------------------------------------------------------------------
    diff = mean(control) - mean(experime)                         t =  -2.2837
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.0112         Pr(|T| > |t|) = 0.0224          Pr(T > t) = 0.9888
