I am looking at the interaction between education (LTHS, HS, SOME COLLEGE, COLLEGE) and race (WHITE, BLACK, HISPANIC, ASIAN, NATIVE AMERICAN). I am using SAS and am including a class statement in my proc genmod (it is a linear binomial model). I am so confused by the output. It gives me estimates for the following:
Less than high school*African American
Less than high school*Hispanic
Less than high school*Asian
Less than high school*Native American
High school*African American
High school*Native American
Some college*African American
Some college*Native American
So what's the reference category? I thought at first it was college-White, but that's not it because it doesn't give me estimates for any of the other races at the college level or whites at the other levels of education. In addition, I am calculating risk differences and when I subtracted mortality per 100,000 in one of the groups from mortality per 100,000 in college educated Whites, it didn't match the betas for risk differences. I think the reference group is anyone who is either white or college educated, but that doesn't seem right.
Does anyone have experience with categorical predictors with >2 levels and interaction? What is the appropriate reference group and how do you specify that in SAS?