
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21802.66    174.4432    22931.82    21460.73    22144.58
experime |  17,281    21845.58    171.8026    22584.69    21508.83    22182.34
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -42.92775    244.8399               -522.8219    436.9664
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    diff = mean(control) - mean(experime)                         t =  -0.1753
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.4304         Pr(|T| > |t|) = 0.8608          Pr(T > t) = 0.5696
