Refer to a study published in the Journal of the American Medical Association and reported in the Sacramento Bee on January 26, 2000 ("Study Ties Hormone Replacement, Cancer" by Shari Roan, p. A1). A sample of 46,355 postmenopausal women were studied for 15 years and asked about their use of hormone therapy and whether or not they had breast cancer; 2082 developed the disease. The article reported that "for each year of combined [estrogen and progestin] therapy, a woman's risk of breast cancer was found to increase by 8 percent compared to a 1 percent increase in women taking estrogen alone."
What are the explanatory and response variables for this study? Are they quantitative or categorical? If they are categorical, what are the categories?