Z table - Normal Distribution
Go to the second graph and type in 0.9 in 'shaded area' and click on 'between' as implies a two tail interval
In the following formula for creating a confidence interval for a mean where do I get from?
I know it has something to do with using z-scores and I've been trying to work backwards from examples. For example a confidence interval of 90% should have but when I look up 0.9 I get 0.8159.