Betsy is interested in predicting how many 75 -year-olds will develop Alzheimer's disease and is using as predictors level of education and general physical health graded on a scale from 1 to 10 . But she is interested in using other predictor variables as well. Answer the following questions.

a. What criteria should she use in the selection of other predictors? Why?

b. Name two other predictors that you think might be related to the development of Alzheimer's disease.

c. With the four predictor variables (level of education, general physical health, and the two new ones that you name), write out the model of the regression equation.