
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21809.31     173.013    22743.81    21470.18    22148.43
experime |  17,281    21838.93    173.2429    22774.03    21499.36    22178.51
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -29.62669      244.84                -509.521    450.2676
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    diff = mean(control) - mean(experime)                         t =  -0.1210
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.4518         Pr(|T| > |t|) = 0.9037          Pr(T > t) = 0.5482
