
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21725.94    172.3061    22650.89     21388.2    22063.68
experime |  17,281     21922.3    173.9428    22866.04    21581.36    22263.25
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -196.3618    244.8377               -676.2517    283.5282
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    diff = mean(control) - mean(experime)                         t =  -0.8020
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2113         Pr(|T| > |t|) = 0.4226          Pr(T > t) = 0.7887
