For data on several nations, we want to describe whether the percentage of people using the Internet is more strongly associated with per capita GDP or with the fertility rate.

(a) Can we compare the slopes when GDP and fertility each predict Internet use in separate regression equations?

Why or why not?

(b) Let x = GDP (thousands of dollars per capita). For recent data on 39 nations from the UN, for y = percentage using cell phones, ˆy = −0.13 + 2.62x, whereas for y percentage using the Internet, ˆy = −3.61 + 1.55x. Why does it make sense to compare these slopes, thus concluding that a one-unit increase in GDP has a slightly greater impact on the percentage using cell phones than on the percentage using the Internet?