
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281     21728.3    171.1373    22497.24    21392.86    22063.75
experime |  17,281    21919.94    175.0931    23017.25    21576.74    22263.14
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            -191.636    244.8378               -671.5261    288.2542
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    diff = mean(control) - mean(experime)                         t =  -0.7827
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2169         Pr(|T| > |t|) = 0.4338          Pr(T > t) = 0.7831
