
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21783.59    171.8743    22594.12     21446.7    22120.48
experime |  17,281    21864.65    174.3722    22922.49    21522.86    22206.44
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -81.06237    244.8396                -560.956    398.8313
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    diff = mean(control) - mean(experime)                         t =  -0.3311
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.3703         Pr(|T| > |t|) = 0.7406          Pr(T > t) = 0.6297
