Chapter 12: Problem 70
In addition to increasingly large bounds on error, why should an experimenter refrain from predicting \(y\) for values of \(x\) outside the experimental region?
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Chapter 12: Problem 70
In addition to increasingly large bounds on error, why should an experimenter refrain from predicting \(y\) for values of \(x\) outside the experimental region?
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Athletes and others suffering the same type of injury to the knee often require anterior and posterior ligament reconstruction. In order to determine the proper length of bone-patellar tendonbone grafts, experiments were done using three imaging techniques to determine the required length of the grafts, and these results were compared to the actual length required. A summary of the results of a simple linear regression analysis for each of these three methods is given in the following table. \({ }^{15}\) $$ \begin{array}{llrcc} \text { Imaging Technique } & \text {Coeffcient of Determination, } r^{2} & \text { Intercept } & \text { Slope } & p \text { -value } \\ \hline \text { Radiographs } & 0.80 & -3.75 & 1.031 & <0.0001 \\ \text { Standard MRI } & 0.43 & 20.29 & 0.497 & 0.011 \\ \text { 3-dimensional MRI } & 0.65 & 1.80 & 0.977 & <0.0001 \end{array} $$ a. What can you say about the significance of each of the three regression analyses? b. How would you rank the effectiveness of the three regression analyses? What is the basis of your decision? c. How do the values of \(r^{2}\) and the \(p\) -values compare in determining the best predictor of actual graft lengths of ligament required?
A marketing research experiment was conducted to study the relationship between the length of time necessary for a buyer to reach a decision and the number of alternative package designs of a product presented. Brand names were eliminated from the packages to reduce the effects of brand preferences. The buyers made their selections using the manufacturer's product descriptions on the packages as the only buying guide. The length of time necessary to reach a decision was recorded for 15 participants in the marketing research study. $$ \begin{array}{l|l|l|l} \begin{array}{l} \text { Length of Decision } \\ \text { Time, } y(\mathrm{sec}) \end{array} & 5,8,8,7,9 & 7,9,8,9,10 & 10,11,10,12,9 \\ \hline \text { Number of } & & & \\ \text { Alternatives, } x & 2 & 3 & 4 \end{array} $$ a. Find the least-squares line appropriate for these data. b. Plot the points and graph the line as a check on your calculations. c. Calculate \(s^{2}\). d. Do the data present sufficient evidence to indicate that the length of decision time is linearly related to the number of alternative package designs? (Test at the \(\alpha=.05\) level of significance.) e. Find the approximate \(p\) -value for the test and interpret its value. f. If they are available, examine the diagnostic plots to check the validity of the regression assumptions. g. Estimate the average length of time necessary to reach a decision when three alternatives are presented, using a \(95 \%\) confidence interval.
The Academic Performance Index (API) is a measure of school achievement based on the results of the Stan- ford 9 Achievement test. Scores range from 200 to 1000 , with 800 considered a long-range goal for schools. The following table shows the API for eight elementary schools in Riverside County, California, along with the percent of students at that school who are considered English Language Learners (ELL). \(^{3}\) $$ \begin{array}{lrrrrrrrr} \text { School } & 1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 \\ \hline \text { API } & 588 & 659 & 710 & 657 & 669 & 641 & 557 & 743 \\ \text { ELL } & 58 & 22 & 14 & 30 & 11 & 26 & 39 & 6 \end{array} $$ a. Which of the two variables is the independent variable and which is the dependent variable? Explain your choice. b. Use a scatterplot to plot the data. Is the assumption of a linear relationship between \(x\) and \(y\) reasonable? c. Assuming that \(x\) and \(y\) are linearly related, calculate the least-squares regression line. d. Plot the line on the scatterplot in part b. Does the line fit through the data points?
What value does \(r\) assume if all the data points fall on the same straight line in these cases? a. The line has positive slope. b. The line has negative slope.
How good are you EX1212 at estimating? To test a subject's ability to estimate sizes, he was shown 10 different objects and asked to estimate their length or diameter. The object was then measured, and the results were recorded in the table below. $$ \begin{array}{lrr} \text { Object } & \text { Estimated (inches) } & \text { Actual (inches) } \\\ \hline \text { Pencil } & 7.00 & 6.00 \\ \text { Dinner plate } & 9.50 & 10.25 \\ \text { Book 1 } & 7.50 & 6.75 \\ \text { Cell phone } & 4.00 & 4.25 \\ \text { Photograph } & 14.50 & 15.75 \\ \text { Toy } & 3.75 & 5.00 \\ \text { Belt } & 42.00 & 41.50 \\ \text { Clothespin } & 2.75 & 3.75 \\ \text { Book 2 } & 10.00 & 9.25 \\ \text { Calculator } & 3.50 & 4.75 \end{array} $$ a. Find the least-squares regression line for predicting the actual measurement as a function of the estimated measurement. b. Plot the points and the fitted line. Does the assumption of a linear relationship appear to be reasonable?
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