1. � For the following pair of variables, which more naturally is the response variable and which is the explanatory variable? College grade point average (GPA) and High school GPA 2. � Use the points on the right to answer the following questions. a. � Find the scores on x and y for each point. Comment on how zx and zy relate to each other for each point. b. � Compute r using the z-scores for the four observations. Is this the value you expected to get for r? Why? 3. � Match the scatterplots to the right with the correlation values. 1. r=0.9 2. r=0.58 3. r=0 4. � The data on the right shows the percent of the population in a country that uses cell phones and their GDP. Let y = cell-phone use x = GDP. a. � The graph on the right shows a scatterplot. Describe this plot in terms of the variability of cell-phone use values for nations close to 0 on GDP. Identify the nation that has less cell-phone use than you would expect, given their GDP. b. � Give the x- and y- coordinates for the nation that has the highest cell-phone use. Give the x- and y- coordinates for the nation that has the highest GDP. c. � Would the correlation be positive , or negative? Explain. d. � Suppose you considered the correlation only for those nations having GDP above 1 Would the correlation be stronger, or weaker, than for all the countries? 5. � For a table of national information it is found that the correlation with Internet use is 0.717 for GDP, 0.533 for cell-phone use, 0.539 for literacy, -0.859 for fertility, and 0.647 for CO2 Emissions. a. � Which variable has the strongest linear association with internet use? b. � Which variable has the weakest linear association with internet use? c. � Interpret the correlation between Internet use and fertility (the mean number of children per adult woman).
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