
Two-sample t test with equal variances
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   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21473.83    169.5944    22294.41    21141.41    21806.25
experime |  17,281    22174.41    176.5508    23208.87    21828.35    22520.47
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -700.5824     244.811                -1180.42   -220.7448
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    diff = mean(control) - mean(experime)                         t =  -2.8617
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.0021         Pr(|T| > |t|) = 0.0042          Pr(T > t) = 0.9979
