14.8 The article “Readability of Liquid Crystal Displays: A Response Surface” (Human Factors [1983]: 185–190)

used a multiple regression model with four independent variables, where y 5 error percentage for subjects reading a fourdigit liquid crystal display x1 5 level of backlight sfrom 0 to 122 cd/md x2 5 character subtense sfrom .025° to 1.34°d x3 5 viewing angle sfrom 0° to 60°d x4 5 level of ambient light sfrom 20 to 1500 lxd The model equation suggested in the article is y 5 1.52 1 .02x1 2 1.40x2 1 .02x3 2 .0006x41e

a. Assume that this is the correct equation. What is the mean value of y when x1 5 10, x2 5 .5, x3 5 50, and x4 5 100?

b. What mean error percentage is associated with a backlight level of 20, character subtense of .5, viewing angle of 10, and ambient light level of 30?

c. Interpret the values of b2 and b3.