Among wedding guests, 50 of the 53 who ate cake became ill. What does the fraction 50 over 53 represent?

1. The denominator counts everyone who ate a particular food, and the numerator counts those among them who fell ill. 2. That is the definition of a food-specific attack rate. 3. A food-specific attack rate is a type of attack rate, which in turn is a synonym for incidence proportion. 4. A secondary attack rate would need cases among contacts of primary cases in the numerator. 5. Period prevalence counts new and pre-existing cases against a population, and proportionate mortality divides deaths from one cause by all deaths, so neither fits. _Source: CDC Principles of Epidemiology in Public Health Practice (3rd ed., US federal, public domain), Lesson 3 "Measures of Risk", section Properties and uses of incidence proportions_