Chapter 8: Problem 1
Explain the difference between a population characteristic and a statistic.
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Chapter 8: Problem 1
Explain the difference between a population characteristic and a statistic.
These are the key concepts you need to understand to accurately answer the question.
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Explain the difference between \(\sigma\) and \(\sigma_{\bar{x}}\) and between \(\mu\) and \(\mu_{\bar{x}}^{-}\)
Consider the following population: \(\\{1,2,3,4\\} .\) Note that the population mean is \(\mu=\frac{1+2+3+4}{4}=2.5\) a. Suppose that a random sample of size 2 is to be selected without replacement from this population. There are 12 possible samples (provided that the order in which observations are selected is taken into account): \(\begin{array}{rrrrrr}1,2 & 1,3 & 1,4 & 2,1 & 2,3 & 2,4 \\ 3,1 & 3,2 & 3,4 & 4,1 & 4,2 & 4,3\end{array}\) Compute the sample mean for each of the 12 possible samples. Use this information to construct the sampling distribution of \(\bar{x}\). (Display the sampling distribution as a density histogram.) b. Suppose that a random sample of size 2 is to be selected, but this time sampling will be done with replacement. Using a method similar to that of Part (a), construct the sampling distribution of \(\bar{x}\). (Hint: There are 16 different possible samples in this case.) c. In what ways are the two sampling distributions of Parts (a) and (b) similar? In what ways are they different?
In the library on a university campus, there is a sign in the elevator that indicates a limit of 16 persons. In addition, there is a weight limit of 2500 pounds. Assume that the average weight of students, faculty, and staff on campus is 150 pounds, that the standard deviation is 27 pounds, and that the distribution of weights of individuals on campus is approximately normal. If a random sample of 16 persons from the campus is to be taken: a. What is the expected value of the distribution of the sample mean weight? b. What is the standard deviation of the sampling distribution of the sample mean weight? c. What average weights for a sample of 16 people will result in the total weight exceeding the weight limit of 2500 pounds? \(\bar{x}>156.25\) d. What is the chance that a random sample of 16 people will exceed the weight limit?
Suppose that a sample of size 100 is to be drawn from a population with standard deviation 10 . a. What is the probability that the sample mean will be within 1 of the value of \(\mu\) ? b. For this example \((n=100, \sigma=10),\) complete each of the following statements by computing the appropriate value: i. Approximately \(95 \%\) of the time, \(\bar{x}\) will be within \(\quad\) of \(\mu\). ii. Approximately \(0.3 \%\) of the time, \(\bar{x}\) will be farther than \(\quad\) from \(\mu\).
The article "Should Pregnant Women Move? Linking Risks for Birth Defects with Proximity to Toxic Waste Sites" (Chance [I992]: \(40-45\) ) reported that in a large study carried out in the state of New York, approximately \(30 \%\) of the study subjects lived within 1 mile of a hazardous waste site. Let \(p\) denote the proportion of all New York residents who live within 1 mile of such a site, and suppose that \(p=.3\). a. Would \(\hat{p}\) based on a random sample of only 10 residents have approximately a normal distribution? Explain why or why not. \(\quad n p=10(0.3)=3<10 .\) b. What are the mean value and standard deviation of \(\hat{p}\) based on a random sample of size \(400 ?\) c. When \(n=400\), what is \(P(.25 \leq \hat{p} \leq .35)\) ? d. Is the probability calculated in Part (c) larger or smaller than would be the case if \(n=500\) ? Answer without actually calculating this probability.
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