
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21708.46    171.2592    22513.25    21372.77    22044.14
experime |  17,281    21939.79    174.9725     23001.4    21596.82    22282.75
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -231.3315    244.8368               -711.2197    248.5567
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    diff = mean(control) - mean(experime)                         t =  -0.9448
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.1724         Pr(|T| > |t|) = 0.3447          Pr(T > t) = 0.8276
