
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21684.79    172.6837    22700.52    21346.31    22023.27
experime |  17,281    21963.45    173.5647    22816.34    21623.25    22303.66
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -278.6623    244.8354               -758.5477    201.2231
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    diff = mean(control) - mean(experime)                         t =  -1.1382
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.1275         Pr(|T| > |t|) = 0.2551          Pr(T > t) = 0.8725
