Figure 9.20 is a scatterplot relating y =percentage of people using cell phones and x = per capita gross domestic product (GDP) for some nations listed in the Human Development Report.

(a) Give the approximate x- and y-coordinates for the nation that has the highest (i) cell phone use, (ii) GDP.

(b) The least squares prediction equation is ˆy = −0.13 +

2.62x. For one nation, x = 34.3 and y = 45.1.

Find the predicted cell-phone use and the residual. Interpret the residual.

(c) Is the correlation positive, or negative? Explain what it means for the correlation to have this sign.

Report, the correlation with percentage of people using the Internet is 0.888 for per capita gross domestic product (GDP, a summary description of a nation’s wealth), 0.818 for percentage using cell phones, 0.669 for literacy rate, −0.551 for fertility rate (the mean number of children per adult woman), and 0.680 for per capita emissions of carbon dioxide.

(a) Explain how to interpret the sign of the correlation between Internet use and (i) GDP, (ii) fertility rate.

(b) Which variable has the (i) strongest, (ii) weakest linear association with Internet use?