
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281     21748.7    171.5039    22545.42    21412.53    22084.86
experime |  17,281    21899.54    174.7352    22970.21    21557.05    22242.04
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -150.8465    244.8387               -630.7383    329.0452
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    diff = mean(control) - mean(experime)                         t =  -0.6161
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2689         Pr(|T| > |t|) = 0.5378          Pr(T > t) = 0.7 311
