If a researcher is studying the relationship between race and educational attainment, and his measure of race is as follows: "Please indicate the racial or ethnic group with which you identify by placing an X in the box to the right of the category to which you belong.

White, non-hispanic

Black, non-hispanic

White, Hispanic

Black, Hispanic

Asian

At what level of measurement does the variable "race" exist? (Note: ignore potential problems with mutual exclusivity or exhaustiveness for this answer).