The Details: Relative risk was a concept Laurel had mentioned in our initial conversation, and so this assignment introduced students to this concept, and asked them to calculate the relative risk of contracting HIV for different racial and ethnic groups in the United States.

On the day we distributed this exercise (see handout.doc), I came into class and reminded the students about the Statistical Abstract of the United States, which was to be their sole source for the numbers they needed to calculate the relative risk of contracting HIV. We had already used the Statistical Abstract in a previous assignment.

Once we reviewed the Statistical Abstract, I spend a couple of moments discussing the content of the handout, highlighting the equation for relative risk (see Figure 1). I also warned students about what challenges they would face in finding the numbers they would need for the assignment. We discussed the fact that racial categorizations taken from the U.S. Census comes with controversy.

Students took the assignment home, and during the next class period, we went over what they had found. At this subsequent class meeting, we compared students' answers (not everyone had come up with the same result). We also discussed the intuition behind what it means to have a relative risk that is greater than or less than 1.

The Downloads: handout (.doc)

(Warning: links on this handout may have changed from the date of original use)

The Goals: From my standpoint, there were two pedagogical goals for this exercise. I wanted students:

• To be able to interpret a relative risk number if they ever saw one in print
• To get a sense of how numbers are used to compare the health of populations of different size

Figure 1: