
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281     21760.6    173.5205    22810.53    21420.48    22100.72
experime |  17,281    21887.64    172.7333    22707.04    21549.07    22226.22
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -127.0438    244.8391               -606.9363    352.8488
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    diff = mean(control) - mean(experime)                         t =  -0.5189
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.3019         Pr(|T| > |t|) = 0.6038          Pr(T > t) = 0.6981
