Before revision: Epidemic model (1927) In its initial form, Kermack–McKendrick theory is a compartmental differential-equation model that structures the infectioned population in terms of age-of-infection, while using simple compartments for people who are susceptible (S) and recovered/removed (R).
After revision: Epidemic model (1927) In its initial form, Kermack–McKendrick theory is a partial differential-equation model that structures the infected, infected (I), population in terms of age-of-infection, while using simple compartments for people who are susceptible (S) and recovered/removed (R).