# HW7 - P-value and your conclusion 3 Using the model that...

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Stat 512 Homework #7 Dr. Levine Due on Friday, Oct 30 th For the next three problems use the data from the truck tire dataset from the course webpage. A testing lab studied the operating costs for trucks driving at various speeds using two makes of tire: A and B. The dataset gives operating cost per mile (Y), cruising speed (X 1 ) and make of tire (X 2 : 0=make A; 1=make B) in that order. 1. Plot the data for the two populations on the same graph, using different symbols ( v= ) and lines. Does the relationship between speed and operating cost appear to be the same for the two makes of tire? 2. Examine the question of whether or not the two lines are the same. Write a model that allows the two makes of tires to have different intercepts and slopes. Then, perform the general linear test to determine whether the two lines are equal. State the null and alternative hypothesis, the test statistic with degrees of freedom, the
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Unformatted text preview: P-value and your conclusion. 3. Using the model that fits two different lines, give a 95% confidence interval for the difference in slopes. (Hint: what parameter represents the difference between the slopes?) 4. For this problem use again the computer science dataset, and fit the model which uses only HSM and HSE as explanatory variables to predict the response GPA. Examine some additional diagnostics for this model that we recently discovered, such as studentized residuals, tolerance or vif, and possibly others. Explain any problems such as outliers, highly influential observations or multicollinearity that these diagnostics point out. ( Do not include in your output any tables of values for all 224 individuals. Use plots and verbal summaries instead. You may include values for a few selected individuals if you wish.)...
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