The following paragraph is from a 1999 USA Today article titled "Heart care reflects race and sex, not symptoms."

"Previous research suggested that blacks and women were less likely than whites and men to get cardiac catheterization or coronary bypass surgery for chest pain or a heart attack. Scientists blamed differences in illness severity, insurance coverage, patient preference, and health care access. The researchers eliminated those differences by videotaping actorstwo black men, two white men, two black women, two white womendescribing chest pain from identical scripts. They wore identical gowns, used identical hand gestures, and were taped from the same position. Researchers asked 720 primary care doctors at meetings of the American College of Physicians or the American Academy of Family Physicians to watch a tape and recommend care. The doctors thought the study focused on clinical decision making."

Researchers rolled a four-sided die to determine which video each doctor watched.

What are the explanatory variables?

• illness severity, insurance coverage, patient preference and health care access
• cardiac catheterization and coronary bypass
• race and sex
• doctors from the American College of Physicians or the American Academy of Family Physicians

What is the response variable?

• illness severity, insurance coverage, patient preference, and healthcare access
• race and sex
• doctors from the American College of Physicians or the American Academy of Family Physicians
• cardiac catheterization and coronary bypass