
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21690.57    170.7689     22448.8    21355.84    22025.29
experime |  17,281    21957.68    175.4496    23064.11    21613.78    22301.57
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -267.1094    244.8358               -746.9955    212.7768
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    diff = mean(control) - mean(experime)                         t =  -1.0910
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.1376         Pr(|T| > |t|) = 0.2753          Pr(T > t) = 0.8624
