
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21728.97    171.4662    22540.47    21392.88    22065.06
experime |  17,281    21919.27    174.7711    22974.92     21576.7    22261.84
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -190.3045    244.8379               -670.1947    289.5857
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    diff = mean(control) - mean(experime)                         t =  -0.7773
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2185         Pr(|T| > |t|) = 0.4370          Pr(T > t) = 0.7815
