SAMPSIZE_p_sp08

# SAMPSIZE_p_sp08 - 5.3 Determining Sample Size to Estimate p...

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5.3 Determining Sample Size to Estimate p

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To Estimate a Population Proportion p If you desire a C% confidence interval for a population proportion p with an accuracy specified by you, how large does the sample size need to be? We will denote the accuracy by SE, which stands for S ampling E rror.
Required Sample Size n to Estimate a Population Proportion p * * * ˆ ± = 2 2 pq CIforp: p z n pq set z SE and solve for n: n z pq n = ; (SE)

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What About p and q= 1- p ? * 2 2 z pq n = ; we don't know p or q; (SE) TWO METHODS: 1: if prior information is available concerning the value of p, use that estimate to calculate n; 2: if no prior information about p is available, to obt = = ain a conservative estimate of the 1 required sample size, use p q 2

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Example: Sample Size to Estimate a Population Proportion p The U. S. Crime Commission wants to estimate p = the proportion of crimes in which firearms are used to within .02 with 90% confidence. Data from previous years shows that p is about .6
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## This note was uploaded on 04/21/2009 for the course BUS 350 taught by Professor Reiland during the Spring '08 term at N.C. State.

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SAMPSIZE_p_sp08 - 5.3 Determining Sample Size to Estimate p...

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