
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21780.59    172.9486    22735.34     21441.6    22119.59
experime |  17,281    21867.65    173.3066    22782.41    21527.95    22207.35
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            -87.0547    244.8396               -566.9482    392.8388
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    diff = mean(control) - mean(experime)                         t =  -0.3556
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.3611         Pr(|T| > |t|) = 0.7222          Pr(T > t) = 0.6389
