
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21928.88    174.2743    22909.61    21587.28    22270.47
experime |  17,281    21719.37    171.9705    22606.76    21382.29    22056.45
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            209.5104    244.8374               -270.3789    689.3998
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    diff = mean(control) - mean(experime)                         t =   0.8557
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.8039         Pr(|T| > |t|) = 0.3922          Pr(T > t) = 0.1961
