
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21659.81    172.1877    22635.32     21322.3    21997.31
experime |  17,281    21988.44    174.0543    22880.69    21647.27     22329.6
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -328.6304    244.8336               -808.5122    151.2515
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    diff = mean(control) - mean(experime)                         t =  -1.3423
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.0898         Pr(|T| > |t|) = 0.1795          Pr(T > t) = 0.9 102
