
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21794.23    172.6946    22701.95    21455.73    22132.73
experime |  17,281    21854.01    173.5601    22815.73    21513.82    22194.21
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -59.78171    244.8398               -539.6757    420.1123
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    diff = mean(control) - mean(experime)                         t =  -0.2442
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.4036         Pr(|T| > |t|) = 0.8071          Pr(T > t) = 0.5964
