
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21632.25    170.2683    22382.99    21298.51       21966
experime |  17,281    22015.99    175.9292    23127.16    21671.15    22360.83
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -383.7352    244.8313               -863.6125    96.14214
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    diff = mean(control) - mean(experime)                         t =  -1.5673
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.0585         Pr(|T| > |t|) = 0.1170          Pr(T > t) = 0.9415
