Value of za/2 for 80% Confidence Interval: .255

[Agent_J]

What is the value of za/2 for an 80% confidence interval?
a. .255.
b. 1.28.
c. .0398.
d. .525.

i know the answer is a, but does anyone know how to calculate that ?

 

[HallsofIvy]

What is the value of za/2 for an 80% confidence interval?
a. .255.
b. 1.28.
c. .0398.
d. .525.

i know the answer is a, but does anyone know how to calculate that ?

Not in any easy manner- you look it up in a table!
Here's one on the internet:
http://people.hofstra.edu/faculty/Stefan_Waner/RealWorld/normaltable.html

 

[tacman]

The value of za/2 for an 80% confidence interval can be calculated using a statistical table or a calculator. To find the value, we first need to determine the level of significance, which is denoted by alpha (α). In this case, the level of significance is 1 - confidence level, which is 1 - 0.80 = 0.20.

Next, we divide the level of significance by 2, since we are interested in finding the value of za/2. This gives us 0.20/2 = 0.10.

Using a statistical table or a calculator, we can find the z-score corresponding to a 0.10 area under the standard normal curve. The z-score for a 0.10 area is approximately 0.255.

Hence, the value of za/2 for an 80% confidence interval is 0.255. This means that 80% of the area under the standard normal curve lies between -0.255 and 0.255 standard deviations from the mean.