Confidence Interval on Difference between Means, Independent Groups, Standard Deviation Known (2 of 3)

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Their scores (in msec) are shown below:

Simple RT: 205, 230, 280, 320, 390
Choice RT: 300, 310, 380, 410, 502, 570

M_Simple = 285 and

M_Choice = 412.

The problem is to estimate the difference between simple and choice reaction time by computing the 95% confidence interval on the difference. The elements required to compute the interval are: the z for the 95% confidence interval, the mean difference (M_d), and the standard error of the mean difference ().

z = 1.96
M_d = 285 - 412 = -127

and =