calulate risk ratio Sick = Number of students who attended the party and got ill: 22 (25 total ill - 3 who did not attend the party) Number of students who attended the party and did not get ill: 304 - 22 = 282. Number of students who did not attend the party and got ill: 3. Number of students who did not attend the party and did not get ill: 4,000 - 304 - 3 = 3,693