
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21764.43    171.3426    22524.22    21428.59    22100.28
experime |  17,281    21883.81    174.8941    22991.09       21541    22226.62
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            -119.372    244.8392               -599.2648    360.5207
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    diff = mean(control) - mean(experime)                         t =  -0.4876
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.3129         Pr(|T| > |t|) = 0.6259          Pr(T > t) = 0.6871
