
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21687.35    171.8494    22590.84    21350.51    22024.19
experime |  17,281    21960.89    174.3911    22924.97    21619.07    22302.72
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -273.5451    244.8356               -753.4308    206.3407
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    diff = mean(control) - mean(experime)                         t =  -1.1173
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.1319         Pr(|T| > |t|) = 0.2639          Pr(T > t) = 0.8681
