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Unformatted text preview: Chapter 18 Sampling Distribution Models ActivStats: 18 Read: Chapter 18 1. Sampling Distribution of Proportion Suppose that p is an unknown proportion of elements of a certain type S in a population For example 1. Proportion of lefthanded people in Michigan 2. Proportion of students at MSU who carry cell phones with them 3. Proportion of voters who will vote for Mr. X in the next election In order to estimate p we select a random sample of size n from the population, compute the number x of elements of type S in the sample and compute the sample proportion n x p = ˆ p ˆ is our estimate of p. Example : Suppose that we want to estimate the proportion p of students in a certain college who carry cell phones with them, and that 187 out of randomly selected 285 students of the college indicated that they had cell phones with them. Then n = 285, x = 187, and % 6 . 65 656 . 285 187 ˆ = = = p is our estimate of p, hence approximately 65.6% of students in this college carry cell phones with them. . QUESTION. What is an error  ˆ  p p of estimation? (Can we answer this without knowledge of real value of p? ) p APPROACH. Suppose that we take another sample of 285 students and compute p ˆ (clearly will be different than 0.656), and then again, and again... 0....
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This note was uploaded on 07/25/2008 for the course STT 200 taught by Professor Dikong during the Summer '08 term at Michigan State University.
 Summer '08
 dikong

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