
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21808.26    174.3583    22920.65     21466.5    22150.02
experime |  17,281    21839.98    171.8889    22596.04    21503.06     22176.9
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -31.71247    244.8399               -511.6068    448.1818
------------------------------------------------------------------------------
    diff = mean(control) - mean(experime)                         t =  -0.1295
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.4485         Pr(|T| > |t|) = 0.8969          Pr(T > t) = 0.5515
