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Homework Help: Chi sqaure & confidence interval

  1. Jun 19, 2008 #1
    Lets say you have 5 trials, and 5 output lets say {5, 43, 60, 30 , 4}....so how would u get the chi sqaure from here & the confidence interval. i havent work on prob &statc in years, thanks a lot for help folks
  2. jcsd
  3. Jun 19, 2008 #2
    I'm supposing you made up this problem... for your random sample of size n=5 is {5, 43, 60, 30 , 4},these are your observed cells/frequencies, but you do not have have your expected cells/frequencies.
  4. Jun 19, 2008 #3
    Basically u can do the confidence for 99%
  5. Jun 19, 2008 #4
    I don't understand what you're trying to do.

    For a Chi-Squared test, you need a null hypothesis and alternative hypothesis.
    The test statistical value is [tex]\chi^2=\sum \frac{(O-E)^2}{E} [/tex]
    where O is a shorthand notation for your observed cells and E is the shorthand notation for expected cell/frequency.

    If you are trying to find the confidence interval for the true variance [tex]\sigma^2[/tex], then the formula for that is

    [tex] P\left( C_{1}< \frac{(n-1)s^2}{\sigma^2} < C_{2} \right) = 1- \alpha[/tex] = .99 since 100(1-alpha)% =99%

    where [tex]C_{1}=\frac{(n-1)s^2}{\chi_{\alpha/2,n-1}}[/tex] is the lower limit
    [tex]C_2 = \frac{(n-1)s^2}{\chi_{1-\alpha/2,n-1}}[/tex] is your upper limit.
    Last edited: Jun 19, 2008
  6. Jun 22, 2008 #5
    lets say u consider #5 as the thresh#, and for the numbers> 5, u tryto find the confiendnce interval for 99.99% or greater. thanks
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