
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21754.81    171.3995     22531.7    21418.85    22090.77
experime |  17,281    21893.43    174.8379     22983.7    21550.73    22236.13
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -138.6245    244.8389               -618.5167    341.2677
------------------------------------------------------------------------------
    diff = mean(control) - mean(experime)                         t =  -0.5662
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2856         Pr(|T| > |t|) = 0.5713          Pr(T > t) = 0.7144
