
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21820.64    174.0387    22878.64    21479.51    22161.77
experime |  17,281     21827.6    172.2125    22638.58    21490.05    22165.16
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -6.964678      244.84               -486.8591    472.9297
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    diff = mean(control) - mean(experime)                         t =  -0.0284
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.4887         Pr(|T| > |t|) = 0.9773          Pr(T > t) = 0.5113
