
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281       21722    170.4526    22407.23     21387.9    22056.11
experime |  17,281    21926.24    175.7593    23104.83    21581.73    22270.74
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -204.2337    244.8375               -684.1233    275.6558
------------------------------------------------------------------------------
    diff = mean(control) - mean(experime)                         t =  -0.8342
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2021         Pr(|T| > |t|) = 0.4042          Pr(T > t) = 0.7979
