
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281     21787.8    174.2404    22905.15    21446.27    22129.33
experime |  17,281    21860.44     172.008     22611.7    21523.29     22197.6
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -72.64438    244.8397               -552.5382    407.2494
------------------------------------------------------------------------------
    diff = mean(control) - mean(experime)                         t =  -0.2967
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.3833         Pr(|T| > |t|) = 0.7667          Pr(T > t) = 0.6167
