# Find Confidence

• June 26th 2010, 06:11 PM
ilikec
Find Confidence
Can someone please give me the final equation for confidence interval for variance when population mean is known.

I only need the equation. Thank you.
• June 26th 2010, 07:27 PM
matheagle
are you assuming normality?
If so, you pivot on

${\sum_{i=1}^n(X_i-\mu)^2\over \sigma^2}\sim\chi^2_n$

${\sum_{i=1}^n(X_i-\bar X)^2\over \sigma^2}\sim\chi^2_{n-1}$
• June 26th 2010, 09:43 PM
mr fantastic
Quote:

Originally Posted by ilikec
Can someone please give me the final equation for confidence interval for variance when population mean is known.

I only need the equation. Thank you.

It is not difficult to find things using Google: http://www.stat.purdue.edu/~tlzhang/...chapter7_4.pdf

How to use Google should be taught at all institutes.
• June 26th 2010, 09:52 PM
matheagle
If you know MOO, then you use

$\sum(X_i-\mu)^2$ instead of $\sum(X_i-\bar X)^2$ and you use n degrees of freedom instead of n-1.
• June 27th 2010, 06:28 AM
ilikec