
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21725.13    172.6007    22689.61    21386.81    22063.44
experime |  17,281    21923.12    173.6505    22827.61    21582.74    22263.49
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -197.9917    244.8377               -677.8816    281.8982
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    diff = mean(control) - mean(experime)                         t =  -0.8087
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2094         Pr(|T| > |t|) = 0.4187          Pr(T > t) = 0.7906
