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Chapter 10: Q. 1.4 (page 633)
Based on your answer to Question , would you be surprised if the difference in the mean amount of liquid dispensed in the two samples wasounces? Explain
No because the probability is very low.
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To study the long-term effects of preschool programs for poor children, researchers designed an experiment. They recruited children who had never attended preschool from low-income families in Michigan. Researchers randomly assigned of the children to attend preschool (paid for by the study budget) and the other to serve as a control group who would not go to preschool. One response variable of interest was the need for social services for adults. In the past years, children in the preschool group and in the control group have needed social services.4 . Does this study provide convincing evidence that preschool reduces the later need for social services? Carry out an appropriate test to help answer this question.
Do drivers reduce excessive speed when they encounter police radar? Researchers studied the behavior of a sample of drivers on a rural interstate highway in Maryland where the speed limit was miles per hour. They measured the speed with an electronic device hidden in the pavement and, to eliminate large trucks, considered only vehicles less than feet long. During some time periods (determined at random), police radar was set up at the measurement location. Here are some of the data.
(a) The researchers chose a rural highway so that cars would be separated rather than in clusters because some cars might slow when they see other cars slowing. Explain why this is important.
(b) Does the proportion of speeding drivers differ significantly when the radar is being used and when it isn’t? Use information from the Minitab computer output below to support your answer.
Refer to Exercise 36. Suppose we select independent SRSs of 16 young men and 9 young women and calculate the sample mean heights
(a) Describe the shape, center, and spread of the sampling distribution of
(b) Find the probability of getting a difference in sample means that’s greater than or equal to inches. Show your work.
(c) Should we be surprised if the sample mean height for the young women is more than inches less than the sample mean height for the young men? Explain.
Find the probability that is less than or equal to . Show your work.
Seat belt use: The proportion of drivers who use seat belts depends on things like age (young people are more likely to go unbelted) and gender (women are more likely to use belts). It also depends on local law. In New York City, police can stop a driver who is not belted. In Boston at the time of the study, police could cite a driver for not wearing a seat belt only if the driver had been stopped for some other violation. Here are data from observing random samples of female Hispanic drivers in these two cities:
(a) Is this an experiment or an observational study? Why?
(b) Construct and interpret a confidence interval for the difference in the proportions of female Hispanic drivers in the two cities who wear seat belts.
(c) Based on the laws in the two cities, we would expect a smaller proportion of drivers to wear seat belts in Boston than in New York. Does the confidence interval in part (b) give good evidence that this is true for female Hispanic drivers? Justify your answer.
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