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Chapter 3

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

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