
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21797.16    171.6008    22558.16     21460.8    22133.51
experime |  17,281    21851.08    174.6417    22957.91    21508.77     22193.4
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -53.92557    244.8398               -533.8196    425.9685
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    diff = mean(control) - mean(experime)                         t =  -0.2202
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.4128         Pr(|T| > |t|) = 0.8257          Pr(T >  t) = 0.5872
