
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21670.23    171.6483     22564.4    21333.78    22006.68
experime |  17,281    21978.01    174.5874    22950.77     21635.8    22320.22
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -307.7819    244.8344               -787.6653    172.1015
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    diff = mean(control) - mean(experime)                         t =  -1.2571
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.1044         Pr(|T| > |t|) = 0.2087          Pr(T > t) = 0.8956
