There are assignments from Statistics by using R-studio.

R Homework for Chapter 18

Motorcycles

More than one million motorcycles are sold annually (www.webbikeworld.com). Off-road motorcycles (often called “dirt bikes”) are a market segment (about 18%) that is highly specialized and offers great variation in features. This makes it a good segment to study to learn about which features account for the cost (manufacturer’s suggested retail price, MSRP) of a dirt bike. Researchers collected data on 2005 model dirt bikes based on a randomized experiment.

You can find the data file on Blackboard. Download it and put it in the same folder as your R program file. Then, use the following command to read in the data motor <- read.table('Motorcycles.txt', sep = '\t', header = TRUE)

and answer the questions below.

1. Let’s take M SRP ($) as response variable and consider W heelbase (in), Displacement (cu in), Bore (in) and Clearance (in) as potential predictors. Use scatterplots to see which variables can be appropriately used as predictors in simple linear regression.

2. Build a multiple regression model for M SRP using Displacement and Bore as predictors. Write down the fitted model. Report R2 and adjusted R2. Interpret the coefficients for Displacement and Bore.

3. Check the model you fitted in the previous question to see if it satisfies the assumptions as required in multiple regression.

4. Conduct a test to see if the fitted multiple regression model is statistically useful. If useful, find the predictors that make significant contributions to the M SRP in the model. Explain.

5. Suppose we are not satisfied with the R2 given by the current model. Please propose a new multiple regression model in order to improve R2. Compare the new model to the current one with respect to their R2, coefficient estimates and hypothesis tests. Don’t forget to check assumptions of the new model for its validity. (Hint: We have two potential predictors W heelbase and Clearance in the pool. Think about how to use them to improve the model.)

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