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91Ó°ÊÓ

Suppose that 500 employees each took a random sample (with replacement) of 100 employees at their office and recorded the salaries of the employees in their sample. Then each employee used his or her data to calculate an \(80 \%\) confidence interval for the mean salary of all employees at the office. How many of the 500 intervals would you expect not to capture the true population mean? Explain by showing your calculation.

Short Answer

Expert verified
Therefore, it is expected that 100 of the 500 intervals would not capture the true population mean.

Step by step solution

01

Understand Confidence Intervals

A confidence interval gives an estimated range of values which is likely to include an unknown population parameter, the estimated range being calculated from a given set of sample data. In this case, each employee creates an \(80 \%\%\) confidence interval for the mean salary, which means they can be \(80 \%\%\) confident that their interval contains the true mean.
02

Calculate the Percentage that does not Capture the True Mean

Since the employees are constructing an \(80 \%\) confidence interval, it logically follows there is a \(20 \%\) chance the confidence interval will not capture the true mean salary. The percentage that would not capture the true mean based on the given confidence level is \(100 \% - 80 \% = 20 \%\). This is because by definition, a \(C \%\) confidence interval will not capture the population parameter in \(100 \% - C \%\) of the cases.
03

Calculate the Number of Intervals Not Capturing the True Mean

To find the expected number of intervals that would not capture the true mean, we multiply the total number of intervals (500) by the percentage calculated in step 2. This is \(500 * 0.2 = 100\).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Statistics Education
Understanding statistics is essential in various fields, ranging from business and economics to public health and sports science. Within the realm of statistics education, the goal is to equip learners with the tools needed to collect, analyze, and interpret data. One fundamental skill taught is how to make inferences about a larger population from a sample. This skill is crucial when dealing with large populations where it's impractical or impossible to collect data from every individual.

By using samples, statisticians can create estimations and predictions about population parameters, such as the mean salary in the given exercise. The exercise depicts a typical scenario students might face: estimating a population mean based on sample data. By tackling such exercises, students gain hands-on experience with the concepts they learn, enhancing their understanding and ability to apply statistical reasoning in real-life situations.
Sampling Distribution
A sampling distribution is a probability distribution of a statistic obtained through a large number of samples drawn from a specific population. It shows how the statistic would vary from one sample to another if you were to keep taking more samples. In the context of the given exercise, each employee's sample can be viewed as one instance drawn from the sampling distribution of the mean salary.

Understanding the sampling distribution is pivotal because it forms the basis for various statistical procedures, including the construction of confidence intervals. It is through this concept that we understand why not all intervals contain the true population mean. This is because the sample mean may differ from the population mean due to sampling variability. Learning about sampling distributions reinforces students' grasp of why confidence intervals provide a range of plausible values for the population mean rather than a single, definitive answer.
Population Mean Estimation
Population mean estimation involves inferring the average outcome of an entire population based on sample data. It's a critical procedure in statistical analysis used to make educated guesses about a population characteristic. For example, in our exercise, the population mean estimation relates to the average salary of all employees in the office.

When constructing an 80% confidence interval for the population mean, there's an implied 20% chance that the interval will not contain the actual population mean. This is because the intervals are constructed using sample data, which has inherent variability. The calculation shown in the step-by-step solution is designed to illustrate how many intervals would typically miss the true mean given the confidence level. This solidifies the concept that confidence intervals are not foolproof guarantees but instead provide a likely range for the true mean based on the sample at hand.

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Most popular questions from this chapter

A McDonald's fact sheet says their cones should weigh \(3.18\) ounces (converted from grams). Suppose you take a random sample of four cones, and the weights are \(4.2,3.4,3.9\), and \(4.4\) ounces. Assume that the population distribution is Normal, and, for all three parts, report the alternative hypothesis, the \(t\) -value, the p-value, and your conclusion. The null hypothesis in all three cases is that the population mean is \(3.18\) ounces. a. Test the hypothesis that the cones do not have a population mean of \(3.18\) ounces. b. Test the hypothesis that the cones have a population mean less than \(3.18\) ounces. c. Test the hypothesis that the cones have a population mean greater than 3.18 ounces.

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Production Time A supervisor of a large factory takes a random sample of 100 laborers from the factory database. He calculates the mean time taken by them to produce one unit of the product. He records this value and repeats the process: He takes another random sample of 100 laborers and calculates the mean time taken. After he has done this 500 times, he makes a histogram of the mean time taken. Is this histogram a display of the population distribution, the distribution of a sample, or the sampling distribution of means?

Even-numbered Digits If you take samples of 25 lines from a C-value table and find that the confidence interval for the proportion of even-numbered digits captures \(95 \% 21\) times out of the 25 lines, is it the confidence interval or confidence level you are estimating with the 21 out of \(25 ?\)

Surfers and statistics students Rex Robinson and Sandy Hudson collected data on the number of days on which surfers surfed in the last month for 30 longboard (L) users and 30 shortboard (S) users. Treat these data as though they were from two independent random samples. Test the hypothesis that the mean days surfed for all longboarders is larger than the mean days surfed for all shortboarders (because longboards can go out in many different surfing conditions). Use a level of significance of \(0.05\). Longboard: \(4,9,8,4,8,8,7,9,6,7,10,12,12,10,14,12,15,13\), \(10,11,19,19,14,11,16,19,20,22,20,22\) Shortboard: \(6,4,4,6,8,8,7,9,4,7,8,5,9,8,4,15,12,10,11\), \(12,12,11,14,10,11,13,15,10,20,20\)

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