Question

Find the critical value  zα/2 that corresponds to the given confidence level 85%

Answer 1

done a similar problem.

Compute the critical value z a/2 that corresponds to 88% confidence level?

ANSWER: 1.55 is STANDARDIZED VARIABLE, z for 88%

Why??

Here's how it works. The 88% confidence level means half (44%) of the confidence interval is below the "mean" and the other half (44%) is the above the"mean".

When you look at a (CUMULATIVE) STANDARD NORMAL DISTRIBUTION TABLE, it shows a column on the left called "z" and it shows a row at the top with twodecimals [.00 .01 .02 .03 . . .].

"z" is positive and negative.


For "z" negative, find "z" = -1.5 on the left of the TABLE; you'll see .0668 And look further right, you'll see .0606 corresponding to "z" = -1.55

"z" negative is half the confidence interval

Guess what??? Sum up .0606 and .0606 = .12, the "a" for
(1 - a) x 100%.