
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    22084.48    177.2599    23302.09    21737.03    22431.92
experime |  17,281    21563.76    168.8719    22199.43    21232.76    21894.77
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            520.7123     244.824                40.84935    1000.575
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    diff = mean(control) - mean(experime)                         t =   2.1269
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.9833         Pr(|T| > |t|) = 0.0334          Pr(T > t) = 0.0167
