stats - really confused about confidence levels

[Guest]

What is the value of za/2 for an 85% confidence interval?

What I did was 1-0.85 = .15/2 = 0.075, then 0.5-0.075 = 0.425, I looked up 0.425 on my stats table and it's 1.44. I belive this would be the same method to calculate the common ones like 95% confidence level = Z.025 = 1.96 correct? But on an online quiz I'm doing, it says the answer is .19 :? ?

 

[rzornick]

I think your problem is that you want to add 0.075 to 0.5 because your confidence level is above 50%. In that case 0.575, according to the chart of z scores I have, would leave you with 0.19. It has been quite a while since I've taken stats so maybe someone else can explain it better.