
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21654.35    171.1059     22493.1    21318.97    21989.74
experime |  17,281    21993.89    175.1173    23020.43    21650.64    22337.14
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -339.5369    244.8332               -819.4179    140.3442
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    diff = mean(control) - mean(experime)                         t =  -1.3868
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.0828         Pr(|T| > |t|) = 0.1655          Pr(T > t) = 0.9172
