
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21851.58    173.5262    22811.28    21511.45    22191.71
experime |  17,281    21796.66    172.7286    22706.43     21458.1    22135.23
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            54.91433    244.8398               -424.9797    534.8084
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    diff = mean(control) - mean(experime)                         t =   0.2243
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.5887         Pr(|T| > |t|) = 0.8225          Pr(T > t) = 0.4113
