Chapter 3 - We can say with 95% confidence that the amount...

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Chapter 3 What Do Samples Tell Us? In this chapter Statistics and parameters Margin of Error Statistics and parameters Statistic – A numerical characteristic of a sample. This value is known when we take our sample, but it will change from sample to sample. Parameter – A numerical characteristic of a population. This value is a fixed number, but when doing inferential statistics we will not know its value. Since the population is often not available, we use statistics to estimate parameters The value of a statistic depends on which items are selected for the sample Therefore, when we take a random sample a statistic is a random variable Variability – Describes the spread of the values We want the possible values of a statistic to not include bias and have a small amount of variability To eliminate bias in a statistic we should use random sampling We can control the variability in a statistic since a larger sample will force less variation Margin of error From the sampling variability we can calculate the margin of error
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Unformatted text preview: We can say with 95% confidence that the amount by which a proportion obtained from a sample will differ from the population proportion will not exceed n 1 Example Suppose you take a sample of 1600 adults and 800 enjoy amusement park rides. 1. What is the sample proportion that enjoy amusement park rides? 2. What is the margin of error? 3. Give a confidence statement for the proportion of all adults who enjoy amusement park rides. Answers 1. % 50 5 . 1600 800 = = 2. % 5 . 2 025 . 40 1 1600 1 1 = = = = n 3. We are 95% confident that the population proportion of adults that enjoy amusement park rides is between 47.5% and 52.5% There are other factors besides sample size that affect the margin of error. However, these factors can always be dealt with by a large enough sample size. The factors follow and will be discussed in detail later in the course. How confident do we want to be in our conclusions How much variability is in our data...
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This note was uploaded on 07/12/2011 for the course STATS 200 taught by Professor Bradley,w during the Fall '10 term at KCTCS.

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Chapter 3 - We can say with 95% confidence that the amount...

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