
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21658.44     172.705    22703.32    21319.92    21996.96
experime |  17,281     21989.8    173.5408     22813.2    21649.64    22329.96
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -331.3612    244.8335               -811.2428    148.5205
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    diff = mean(control) - mean(experime)                         t =  -1.3534
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.0880         Pr(|T| > |t|) = 0.1759          Pr(T > t) = 0.9120
