Pagano and Gauvreau (1993, p. 133) reported data for women participating in the first National Health and Nutrition Examination Survey (Carter et al., 1989). The explanatory variable was whether or not the woman gave birth to her first child at the age of 25 or older, and the outcome variable was whether or not she developed breast cancer. Observed counts are in the following table.
a. Calculate the risk of breast cancer for women who were under 25 years old when they had their first child.
b. Calculate the risk of breast cancer for women who were 25 or older when they had their first child.
c. Calculate the relative risk of breast cancer for women who were 25 or older when they had their first child compared with women who were under 25. Write a sentence that interprets this relative risk in the context of this problem.
d. What is the percent increase in the risk of breast cancer for women who were 25 or older when they had their first child?
e. Can these data be used as evidence of a causal connection between age at first child and the risk of breast cancer? Explain.