11.5. A regression analysis with recent UN data from several nations on y = percentage of people who use the Internet, X| = per capita gross domestic product (in thousands of dollars), and X2 = percentage of people using cell phones has results shown in Table 11.11.

(a) Write the prediction equation.

(b) Find the predicted Internet use for a country with per capita GDPof $ 10,000 and 50% using cell phones.

(c) Find the prediction equations when cell-phone use is (i) 0 %, (ii) 100%, and use them to interpret the effect of GDP.

(d) Use the equations in

(c) to explain the "no interaction" property of the model.

TABLE 11.11 B Std. Error t Sig

(Constant) -3.601 2.506 -1.44 0.159 GDP 1.2799 0.2703 4.74 0.000 CELLULAR 0.1021 0.0900 1.13 0.264 R Square .796 ANOVA Sum of Squares DF Regression 10316.8 2 Residual Error 2642.5 36 Total 12959.3 38