
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281     21757.8     175.053    23011.98    21414.68    22100.92
experime |  17,281    21890.44    171.1799    22502.83    21554.91    22225.97
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -132.6463     244.839               -612.5387     347.246
------------------------------------------------------------------------------
    diff = mean(control) - mean(experime)                         t =  -0.5418
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2940         Pr(|T| > |t|) = 0.5880          Pr(T > t) = 0.7060
