
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21934.77     174.629    22956.24    21592.47    22277.06
experime |  17,281    21713.48    171.6098    22559.35     21377.1    22049.85
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            221.2888    244.8371               -258.5999    701.1776
------------------------------------------------------------------------------
    diff = mean(control) - mean(experime)                         t =   0.9038
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.8170         Pr(|T| > |t|) = 0.3661          Pr(T > t) = 0.1830
