
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21752.54    173.0919    22754.19    21413.26    22091.82
experime |  17,281     21895.7    173.1624    22763.45    21556.28    22235.12
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -143.1579    244.8388                 -623.05    336.7341
------------------------------------------------------------------------------
    diff = mean(control) - mean(experime)                         t =  -0.5847
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.2794         Pr(|T| > |t|) = 0.5588          Pr(T > t) = 0.7206
