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Statistics: Confidence Intervals

  1. Jul 7, 2008 #1
    The problem in question is as follows:

    Find themargin of error for the given values of c, s, and n. where c is the confidence interval, s is the sample standard deviation and n is the number of objects.

    c=0.65 s= 1.5 n=50

    the formula: E= (zc s) / n^.5

    Level of Confidence Chart

    c ........................zc
    .80.......................1.28
    .90.......................1.645
    .95........................1.96
    .99.........................2.575


    As you can see, the zc value for c=.65 is not present on the chart. I don't know how to proceed to solve the problem by finding the corresponding zc for when c=.65. if anyone could show me, that would be appreciated.
    thankx
     
  2. jcsd
  3. Aug 13, 2008 #2
    [tex]z_{c}=0.93[/tex] for [tex]c=0.65[/tex]. Easy to find on your table for the Standard Normal Distribution.
     
  4. Aug 30, 2008 #3
    Hey LearnFrench,

    How do they determine the 0.93 statistic in the first place? Assuming I have no life, how could I derive a table on my own?

    Thanks,
    HF08
     
  5. Aug 31, 2008 #4

    CRGreathouse

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    Science Advisor
    Homework Helper

    Numerical integration of the normal distribution's pdf would probably be the easiest way. The more traditional but also more complex way would start with the error function.
     
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