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Chapter 8: Q 2. (page 506)
Got shoes? The class in Exercise 1 wants to estimate the variability in the number of pairs
of shoes that female students have by estimating the population standard deviation .
The standard deviation is
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Bone loss by nursing mothers Breast-feeding mothers secrete calcium into
their milk. Some of the calcium may come from their bones, so mothers may lose bone mineral. Researchers measured the percent change in bone mineral content (BMC) of the spines of randomly selected mothers during three months of breast-feeding. The mean change in BMC was and the standard deviation was
a. Construct and interpret a confidence interval to estimate the mean percent change in BMC in the population of breast-feeding mothers.
b. Based on your interval from part (a), do these data give convincing evidence thatnursing mothers lose bone mineral, on average? Explain your answer.
Price cuts (4.2) Stores advertise price reductions to attract customers. What type of price
cut is most attractive? Experiments with more than one factor allow insight into
interactions between the factors. A study of the attractiveness of advertised price discounts
had two factors: percent of all foods on sale (25%, 50%, 75%, or 100%) and whether the discount was stated precisely (e.g., as in “60% off”) or as a range (as in “40% to 70% off”). Subjects rated the attractiveness of the sale on a scale of 1 to 7.
a. List the treatments for this experiment, assuming researchers will use all combinations of the two factors.
b. Describe how you would randomly assign 200 volunteer subjects to treatments.
c. Explain the purpose of the random assignment in part (b).
d. The figure shows the mean ratings for the eight treatments formed from the two factors.35 Based on these results, write a careful description of how percent on sale and precise discount versus range of discounts influence the attractiveness of a sale.
Refer to Exercise 55. Suppose that Gallup wanted to cut the margin of error in half from percentage points to percentage points. How should they adjust their sample size?
a. Multiply the sample size by .
b. Multiply the sample size by .
c. Multiply the sample size by .
d. Multiply the sample size by .
e. There is not enough information to answer this question.
Judy is interested in the reading level of a medical journal. She records the length of a random sample ofwords. The histogram displays the distribution of word length for her sample. Determine if the Normal/Large Sample condition is met in this context.
The U.S. Forest Service is considering additional restrictions on the number of vehicles allowed to enter Yellowstone National Park. To assess public reaction, the service asks a random sample of 150 visitors if they favor the proposal, Of these, 89 say "Yes."
a. Construct and interpret a confidence interval for the proportion of all visitors to Yellowstone who favor the restrictions.
b. Based on your work in part (a), is there convincing evidence that more than half of all visitors to Yellowstone National Park favor the proposal? Justify your answer.
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