Chapter 8: Q.3.4 (page 511)
Interpret your interval in context.
There is probability that the mean healing rate is between and
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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 and whether the discount was stated precisely (as in, for example, off”) or as a range (as in “to off”). Subjects rated the attractiveness of the sale on a scale of 1 to 7. (a) Describe a completely randomized design using student subjects. (b) Explain how you would use the partial table of random digits below to assign subjects to treatment groups. Then use your method to select the first subjects for one of the treatment groups. Show your work clearly on your paper.
(c) The figure below shows the mean ratings for the eight treatments formed from the two factors. 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.
Reporting cheating What proportion of students are willing to report cheating by other students? A student project put this question to an SRS of undergraduates at a large university: “You witness two students cheating on a quiz. Do you go to the professor?” Only 19 answered “Yes.”
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 breastfeeding. 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.
(b) Based on your interval from (a), do these data give good evidence that on average nursing mothers lose bone mineral? Explain.
59.Blood pressure A medical study finds that and for the seated systolic blood pressure of the members of one treatment group. What is the standard error of the mean? Interpret this value in context.
Prayer in school A New York Times/CBS News Poll asked the question, “Do you favor an amendment to the Constitution that would permit organized prayer in public schools?” Sixty-six percent of the sample answered “Yes.” The article describing the poll says that it “is based on telephone interviews conducted from Sept. 13 to Sept. 18 with adults around the United States, excluding Alaska and Hawaii. . . . The telephone numbers were formed by random digits, thus permitting access to both listed and unlisted residential numbers.” The article gives the margin of error for a confidence level as percentage points.
(a) Explain what the margin of error means to someone who knows little statistics.
(b) State and interpret the 95% confidence interval.
(c) Interpret the confidence level.
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