
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21580.34    170.8019    22453.14    21245.55    21915.13
experime |  17,281     22067.9    175.4037    23058.09    21724.09    22411.71
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -487.5552     244.826                -967.422   -7.688311
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    diff = mean(control) - mean(experime)                         t =  -1.9914
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.0232         Pr(|T| > |t|) = 0.0464          Pr(T > t) = 0.9768
