
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    22000.39    175.2069    23032.21    21656.97    22343.82
experime |  17,281    21647.85    171.0134    22480.94    21312.64    21983.05
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |            352.5454    244.8327               -127.3346    832.4254
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    diff = mean(control) - mean(experime)                         t =   1.4399
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.9251         Pr(|T| > |t|) = 0.1499          Pr(T > t) = 0.0749
