
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21933.43    174.5807     22949.9    21591.24    22275.63
experime |  17,281    21714.81     171.659    22565.82    21378.34    22051.28
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            218.6245    244.8372               -261.2643    698.5134
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    diff = mean(control) - mean(experime)                         t =   0.8929
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.8141         Pr(|T| > |t|) = 0.3719          Pr(T > t) = 0.1859
