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November 28th, 2015, 05:55 AM  #1 
Newbie Joined: Nov 2015 From: HK Posts: 8 Thanks: 0  sample size for confidence interval
Question: A state legistlator wishes to survey residents of her district to see what proportion of the electorate is aware of her position on using state funds to pay for abortions. What sample size is necessary if the 95% confidence interval for p is to have width at most 0.10 irrespective of p? (p bar) + Z0.025 sigma/sqrt(n)  (p bar  Z0.025 sigma / sqrt(n)) <= 0.1 2(Z0.025 sigma/ sqrt(n) ) <= 0.1 but sigma is not known Last edited by tttim; November 28th, 2015 at 06:27 AM. 
November 28th, 2015, 02:50 PM  #2 
Global Moderator Joined: May 2007 Posts: 6,754 Thanks: 695 
Sigma is a function of p and n (binomial distribution). Fixing sigma leaves n dependent on p.


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confidence, interval, sample, size 
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