
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21585.32    169.9539    22341.66    21252.19    21918.45
experime |  17,281    22062.92    176.2263    23166.22     21717.5    22408.34
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -477.6048    244.8265               -957.4727    2.263221
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    diff = mean(control) - mean(experime)                         t =  -1.9508
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.0255         Pr(|T| > |t|) = 0.0511          Pr(T > t) = 0.9745
