
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21536.33    170.5618    22421.58    21202.01    21870.65
experime |  17,281    22111.91    175.6295    23087.76    21767.66    22456.16
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -575.5768    244.8204               -1055.433   -95.72082
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    diff = mean(control) - mean(experime)                         t =  -2.3510
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.0094         Pr(|T| > |t|) = 0.0187          Pr(T > t) = 0.9906
