
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21796.15    173.3219    22784.41    21456.43    22135.88
experime |  17,281    21852.09    172.9337    22733.38    21513.12    22191.05
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            -55.9324    244.8398               -535.8264    423.9616
------------------------------------------------------------------------------
    diff = mean(control) - mean(experime)                         t =  -0.2284
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.4097         Pr(|T| > |t|) = 0.8193          Pr(T > t) = 0.5903
