Results 1 to 6 of 6

Math Help - Find Confidence

  1. #1
    Junior Member
    Joined
    May 2010
    Posts
    39

    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.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor matheagle's Avatar
    Joined
    Feb 2009
    Posts
    2,763
    Thanks
    5
    are you assuming normality?
    If so, you pivot on

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

    instead of

    {\sum_{i=1}^n(X_i-\bar X)^2\over \sigma^2}\sim\chi^2_{n-1}
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by ilikec View Post
    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.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor matheagle's Avatar
    Joined
    Feb 2009
    Posts
    2,763
    Thanks
    5
    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.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Junior Member
    Joined
    May 2010
    Posts
    39
    well now i need to know how to prove it. please help.
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by ilikec View Post
    well now i need to know how to prove it. please help.
    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 ....
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Find Confidence Level of Coefficients
    Posted in the Advanced Statistics Forum
    Replies: 0
    Last Post: March 9th 2011, 12:08 PM
  2. How to find zα/2 values for confidence interval
    Posted in the Advanced Statistics Forum
    Replies: 1
    Last Post: February 17th 2011, 06:06 PM
  3. confidence level and confidence interval?
    Posted in the Advanced Statistics Forum
    Replies: 2
    Last Post: July 12th 2009, 07:59 AM
  4. Find 90% confidence interval
    Posted in the Advanced Statistics Forum
    Replies: 8
    Last Post: June 16th 2009, 08:04 AM
  5. Find 99% confidence interval estimate of....
    Posted in the Advanced Statistics Forum
    Replies: 0
    Last Post: December 20th 2005, 07:23 AM

Search Tags


/mathhelpforum @mathhelpforum