I know a 90% confidence interval is between [1.527, 1.632] that’s it. And I need to find the limits for a 95% Confidence interval how do you do this?
I only know the limits, that is has a normal distribution and the standard deviation has a value of σ.
I’ve tried looking online and in a textbook and I’ve found NOTHING
In: Mathematics
You use Z-tables, pretty surprised you didn’t find anything, as you literally just need to good the formula for a confidence interval……. nerdy judgemental stare…
What you do is luck up the z-score in a z-table for the 95% percentile (check your text book on that). *hint* it’s a number around ~~1.5-1.6~~ 1.2-1.3. As I was reminded – this is a *double sided* score. I always screw that up.
you take your sample mean, plus or minus the z-score multiplied by the (sample SD) / (square-root sample size)
I think the challenge to this math problem isn’t the formula, it might be finding the values you don’t know based on the 90% interval and then reusing them for the 95% calculation.
For example, you didn’t mention you knew the sample size. The sample mean is just in the middle of the interval you have, so that’s the sample mean. The 90% Z-score can also be found in a table. So you can calculate the sample size based on the 90% and then use that for your 95% problem.
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