13.8 ● Hormone replacement therapy (HRT) is thought to increase the risk of breast cancer. The accompanying data on x 5 percent of women using HRT and y 5 breast cancer incidence (cases per 100,000 women) for a region in Germany for 5 years appeared in the paper “Decline in Breast Cancer Incidence after Decrease in Utilisation of Hormone Replacement Therapy” (Epidemiology [2008]:

427–430). The authors of the paper used a simple linear regression model to describe the relationship between HRT use and breast cancer incidence.

HRT Use Breast Cancer Incidence 46.30 103.30 40.60 105.00 HRT Use Breast Cancer Incidence 39.50 100.00 36.60 93.80 30.00 83.50

a. What is the equation of the estimated regression line?

b. What is the estimated average change in breast cancer incidence associated with a 1 percentage point increase in HRT use?

c. What would you predict the breast cancer incidence to be in a year when HRT use was 40%?

d. Should you use this regression model to predict breast cancer incidence for a year when HRT use was 20%? Explain.

e. Calculate and interpret the value of r2.

f. Calculate and interpret the value of se.