My Math Forum sample size for confidence interval

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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: 6,806 Thanks: 716 Sigma is a function of p and n (binomial distribution). Fixing sigma leaves n dependent on p.

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