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assign2 - Winter 2011/12 Term 1 Statistics 200 Assignment#2...

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Winter 2011/12 Term 1 Statistics 200 Assignment #2 Due: 5pm on Friday Oct 14, 2011 (Total mark: 50) 1. Consider the data in the file alcohol.xls . These are data from a British government survey of house- hold spending. We are interested in the relationship between household spending on tobacco products and alcholic beverages. This problem illustrates the effect that a single influential observation might have on a least-squares regression fit. Note: You may do this question by hand or by using Excel. (a) Draw a scatter plot of ”Alcohol” as function of ”Tobacco”. (1 mark) (b) Compute the intercept and slope for the corresponding least squares linear regression line. (1 mark) (c) Add the regression line to the previous plot. Also obtain the residual plot. Is a linear relationship between these variables reasonable? Do you see any atypical or outlying point? (3 marks) (d) Repeat (a), (b) and (c) above without using the observation from Northern Ireland. (5 marks) (e) Which of the two linear regression lines (the one obtained with all the data and the one without Northern Ireland) provides a better fit to the data from the first ten regions in the dataset? Briefly justify your answer. (2 marks) 2. A school nurse is interested in studying the relationship between blood type and dairy allergy in children. She retrieves the health records of all 785 children in the school that she works in. Information about the blood type and whether each child has dairy allergy are summarized in the following two-way

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assign2 - Winter 2011/12 Term 1 Statistics 200 Assignment#2...

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