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 error percentage for subjects reading a fourdigit liquid crystal display x1 level of backlight (from 0 to 122 cd/m)

x2 character subtense (from .025° to 1.34°)

x3 viewing angle (from 0° to 60°)

x4 level of ambient light (from 20 to 1500 lx)

The model equation suggested in the article is y 5 1.52 1 .02x1 2 1.40x2 1 .02x3 2 .0006x4 1 e

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