
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21897.16    174.3609    22920.99    21555.39    22238.92
experime |  17,281    21751.09    171.8846    22595.47    21414.17       22088
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            146.0708    244.8387               -333.8211    625.9628
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    diff = mean(control) - mean(experime)                         t =   0.5966
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.7246         Pr(|T| > |t|) = 0.5508          Pr(T > t) = 0.2754
