
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21718.54     171.975    22607.36    21381.45    22055.63
experime |  17,281     21929.7    174.2697    22909.01    21588.12    22271.29
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -211.1665    244.8374               -691.0557    268.7228
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    diff = mean(control) - mean(experime)                         t =  -0.8625
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.1942         Pr(|T| > |t|) = 0.3884          Pr(T > t) = 0.8058
