Is participating in a follow-up survey associated with having medical aid? Exercise 19.1 considered whether participation in a follow-up survey was associated with having medical aid. Race was a confounding variable in this analysis. Table 19.5 lists both crude and race-specific cross tabulations.

(a) Calculate the race-specific prevalence ratios (“relative risks”)

for medical aid. Do you think statistical interaction is present?

(b) Conduct a chi-square test of interaction for the prevalence ratios. Show all hypothesis-testing steps. Report the , its df, and P-value. Is the opinion you formed about interaction in part

(a) of the exercise confirmed?