6167SU09HW2 - STA 6167 Homework Assn #2 Spring 2007 1....

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STA 6167 Homework Assn #2 Spring 2007 1. Following are data from problem 12.12 in Ott and Longnecker (2001). The values in column 1 are rpm settings of a machine used for testing wear of a fabric, and the values in columns 2-9 are measures of wear from replicate runs. 100 23.0 23.5 24.4 25.2 25.6 26.1 24.8 25.6 120 26.7 26.1 25.8 26.3 27.2 27.9 28.3 27.4 140 28.0 28.4 27.0 28.8 29.8 29.4 28.7 29.3 160 32.7 32.1 31.9 33.0 33.5 33.7 34.0 32.5 180 43.1 41.7 42.4 42.1 43.5 43.8 44.2 43.6 200 54.2 43.7 53.1 53.8 55.6 55.9 54.7 54.5 a. Plot the values of WEAR versus RPM. Describe the patterns you observe. b. Fit a linear regression model to relate WEAR to RPM. Write the fitted equation. c. Plot the residuals versus predicted values from the fitted linear regression. Does the linear model seem appropriate? d. Fit a quadratic model to relate WEAR to RPM. Write the fitted equation. e. Does the quadratic equation fit “significantly better” than the linear equation? f. Plot residuals from the quadratic equation. Do you detect outliers? g. Remove outliers from the data set and refit the quadratic model. Compare predicted values of the quadratic fitted with and without the outlier. Where do you see the most effect?
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6167SU09HW2 - STA 6167 Homework Assn #2 Spring 2007 1....

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