
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21719.77    170.2036    22374.49    21386.15    22053.38
experime |  17,281    21928.47    176.0003    23136.51     21583.5    22273.45
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -208.7065    244.8374               -688.5958    271.1829
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    diff = mean(control) - mean(experime)                         t =  -0.8524
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.1970         Pr(|T| > |t|) = 0.3940          Pr(T > t) = 0.8 030
