
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21586.66    169.4881    22280.44    21254.44    21918.87
experime |  17,281    22061.58    176.6745    23225.14    21715.28    22407.88
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -474.9276    244.8267               -954.7958    4.940699
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    diff = mean(control) - mean(experime)                         t =  -1.9399
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.0262         Pr(|T| > |t|) = 0.0524          Pr(T > t) = 0.9738
