
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281     21748.7    174.6051     22953.1    21406.46    22090.95
experime |  17,281    21899.54    171.6363    22562.83    21563.11    22235.96
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -150.8355    244.8387               -630.7272    329.0563
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    diff = mean(control) - mean(experime)                         t =  -0.6161
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2689         Pr(|T| > |t|) = 0.5379          Pr(T > t) = 0.7311
