Question

Which of the following is the upper critical value of z (z*) for an 80% confidence interval?

a. 1.96
b. .84
c. 2.33
d. 1.45
e. 1.28

Answer 1

e. 1.28

Explanation:

We have that to find our
`\alpha` level, that is the subtraction of 1 by the confidence interval divided by 2. So:

`\alpha = (1-0.8)/(2) = 0.1`

Now, we have to find z in the Ztable as such z has a pvalue of
`1-\alpha`. This is our critical value.

So it is z with a pvalue of
`1-0.1 = 0.9`, so
`z = 1.28`

The correct answer is:

e. 1.28