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Press
@HELP
to obtain a screen explaining the meaning of the confidence interval
in terms of random numbers generated by a calculator. To scroll down the
resulting screen use the down-arrow key ˜. Press @@@OK@@@ when done with the
help screen. This will return you to the screen shown above.
To calculate the confidence interval, press @@@OK@@@. The result shown in the
calculator is:
The result indicates that a 95% confidence interval has been calculated. The
Critical z value shown in the screen above corresponds to the values ±z
α/2
in
the confidence interval formula (⎯X−z
α/2
⋅σ/√n , ⎯X+z
α/2
⋅σ/√n ). The values μ
Min and μ Max are the lower and upper limits of this interval, i.e., μ Min = ⎯X−
z
α/2
⋅σ/√n, and μ Max = ⎯X+z
α/2
⋅σ/√n.
Press @GRAPH to see a graphical display of the confidence interval information:
The graph shows the standard normal distribution pdf (probability density
function), the location of the critical points ±z
α/2
, the mean value (23.3) and the
corresponding interval limits (21.98424 and 24.61576). Press @TEXT to return
to the previous results screen, and/or press @@@OK@@@ to exit the confidence interval
environment. The results will be listed in the calculator’s display.