
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21878.14    173.6126    22822.63    21537.84    22218.44
experime |  17,281     21770.1    172.6411    22694.92    21431.71     22108.5
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            108.0325    244.8393               -371.8605    587.9256
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    diff = mean(control) - mean(experime)                         t =   0.4412
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.6705         Pr(|T| > |t|) = 0.6590          Pr(T > t) = 0.3295
