CI_p_sp08 - LECTURE UNIT 5 Confidence Intervals...

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LECTURE UNIT 5 Confidence Intervals (application of the Central Limit Theorem) Sections 5.1, 5.2 Introduction and Confidence Intervals for Proportions
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Concepts of Estimation The objective of estimation is to estimate the unknown value of a population parameter , like a population proportion p, on the basis of a sample statistic calculated from sample data. e.g., NCSU student affairs office may want to estimate the proportion of students that want more campus weekend activities There are two types of estimates Point Estimate Interval estimate
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Point Estimate of p p = , the sample proportion of x successes in a sample of size n, is the best point estimate of the unknown value of the population proportion p ^ n x
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Example: Estimating an unknown population proportion p Is Herb Sendek's departure good or bad for State's men's basketball team? ( Technician opinion poll; not scientifically valid!!) In a sample of 1000 students, 590 say that Sendek’s departure is good for the bb team. p = 590/1000 = .59 is the point estimate of the unknown population proportion p that think Sendek’s departure is good. ^
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Shortcoming of Point Estimates p = 590/1000 = .59, best estimate of population proportion p BUT How good is this best estimate? No measure of reliability ^ Another type of estimate
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is a range (or an interval) of values used to estimate the unknown value of a population parameter . http://abcnews.go.com/US/PollVault/
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CI_p_sp08 - LECTURE UNIT 5 Confidence Intervals...

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