The article "Readability of Liquid Crystal Displays: A Response Surface" (Human Factors [1983]: 185-190) used an estimated regression equation to describe the relationship between y = error percentage for subjects reading a four-digit liquid crystal display and the independent variables x1 = level of backlight, x2 = character subtense, x3 = viewing angle, and x4 = level of ambient light. From a table given in the article, SSRegr = 19.2, SSResid = 20.0, and n = 30.
a. Does the estimated regression equation specify a useful relationship between y and the independent variables? Use the model utility test with a .05 significance level.
b. Calculate R2 and se for this model. Interpret these values.
c. Do you think that the estimated regression equation would provide reasonably accurate predictions of error percentage? Explain