
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21767.63    172.7055    22703.39    21429.11    22106.15
experime |  17,281    21880.61    173.5484    22814.19    21540.44    22220.78
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            -112.975    244.8393               -592.8679    366.9179
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    diff = mean(control) - mean(experime)                         t =  -0.4614
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.3222         Pr(|T| > |t|) = 0.6445          Pr(T > t) = 0.6778
