Domestic water and dental cavities, range restriction. Another way to look at the data presented in Exercise 14.6 is to restrict the analysis to a range that can be described with a straight line. This is called a range restriction.

(a) Use the scatterplot you drew in Exercise 14.6

(a) to determine whether there is a range of FLUORIDE in which the relationship between FLUORIDE and CARIES is fairly straight. Restrict the data to this range. Then determine the least squares line for this segment of the data. Interpret b.

(b) Calculate r 2 for this range-restricted model. Which model has a better fit, this model or the ln–ln transformed model from the previous exercise?

(c) Which model do you prefer, this model or the one created in Exercise 14.6? Explain your reasoning.