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Chapter 12: Q. 25 (page 764)
Confidence intervals and tests for these data use the t distribution with degrees of freedom
(a) 9.29.
(c) 15.
(e) 30.
(b) 14.
(d) 16.
(b) 14
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Explain why it would be reasonable to use an exponential model to describe the relationship between the U.S. population in the years to and the number of years since . Here is some Minitab output from a linear regression analysis on the transformed data.
A confidence interval for the population slope is
(a) .
(b) .
(c) .
(d) .
(e) .
Foresters are interested in predicting the amount of usable lumber they can harvest from various tree species. They collect data on the diameter at breast height (DBH) in inches and the yield in board feet of a random sample of Ponderosa pine trees that have been harvested. (Note that a board foot is defined as a piece of lumber inches by inches by inch.) A scatterplot of the data is shown below
(a) Some computer output and a residual plot from a least squares regression on these data appear below. Explain why a linear model may not be appropriate in this case.
(B) Use both models to predict the amount of usable lumber from a Ponderosa pine with diameter inches. Show your work.
(c) Which of the predictions in part (b) seems more reliable? Give appropriate evidence to support your choice.
Give the equation of the least-squares regression line. Define any variables you use.
A study of road rage asked random samples of men and women about their behavior while driving. Based on their answers, each respondent was assigned a road rage score on a scale of to . The respondents were chosen by random digit dialing of telephone numbers. Are the conditions for two-sample t inference satisfied?
(a) Maybe. The data came from independent random samples, but we need to examine the data to check for Normality.
(b) No. Road rage scores in a range between and can鈥檛 be Normal.
(c) No. A paired t test should be used in this case.
(d) Yes. The large sample sizes guarantee that the corresponding population distributions will be Normal.
(e) Yes. We have two independent random samples and large sample sizes, and the condition is met.
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