
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281     21848.2    171.8297    22588.25     21511.4       22185
experime |  17,281    21800.04    174.4165    22928.31    21458.17    22141.92
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            48.15791    244.8399               -431.7362     528.052
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    diff = mean(control) - mean(experime)                         t =   0.1967
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.5780         Pr(|T| > |t|) = 0.8441          Pr(T > t) = 0.4220
