
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21797.03    174.5988    22952.27     21454.8    22139.26
experime |  17,281    21851.21    171.6444     22563.9    21514.77    22187.65
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -54.17568    244.8398               -534.0697    425.7184
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    diff = mean(control) - mean(experime)                         t =  -0.2213
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.4124         Pr(|T| > |t|) = 0.8249          Pr(T > t) = 0.5876
