
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21783.09    172.3132    22651.81    21445.34    22120.84
experime |  17,281    21865.15    173.9385    22865.47    21524.22    22206.09
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -82.06347    244.8396               -561.9571    397.8301
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    diff = mean(control) - mean(experime)                         t =  -0.3352
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.3687         Pr(|T| > |t|) = 0.7375          Pr(T > t) = 0.6313
