
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21714.78    171.2412    22510.89    21379.13    22050.43
experime |  17,281    21933.47    174.9906    23003.77    21590.47    22276.47
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -218.6901    244.8372               -698.5789    261.1988
------------------------------------------------------------------------------
    diff = mean(control) - mean(experime)                         t =  -0.8932
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.1859         Pr(|T| > |t|) = 0.3718          Pr(T > t) = 0.8141
