
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21797.67    173.2029    22768.77    21458.17    22137.16
experime |  17,281    21850.58    173.0529    22749.05    21511.38    22189.78
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            -52.9111    244.8398               -532.8052     426.983
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    diff = mean(control) - mean(experime)                         t =  -0.2161
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.4145         Pr(|T| > |t|) = 0.8289          Pr(T > t) = 0.5855
