# Find Confidence

• Jun 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.
• Jun 26th 2010, 07:27 PM
matheagle
are you assuming normality?
If so, you pivot on

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

${\sum_{i=1}^n(X_i-\bar X)^2\over \sigma^2}\sim\chi^2_{n-1}$
• Jun 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.
• Jun 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.
• Jun 27th 2010, 06:28 AM
ilikec
• Jun 27th 2010, 02:08 PM
mr fantastic
Quote:

Originally Posted by ilikec

Did you read the link I gave you? You give no indication of how detailed a proof is required - the link I gave you ought to be good enough. And in your original post you said you only wanted the final equation. Please state clearly right from the start what the actual question is next time.

You will find this stuff and more in most statistics books. A bit more effort on your part would not go astray. You could do worse things than visit your institute's library ....
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