
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21873.68    174.0398    22878.78    21532.55    22214.82
experime |  17,281    21774.56    172.2106    22638.33    21437.01    22112.11
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            99.12691    244.8394               -380.7663    579.0202
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    diff = mean(control) - mean(experime)                         t =   0.4049
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.6572         Pr(|T| > |t|) = 0.6856          Pr(T > t) = 0.3428
