Main variables used in outbreak severity measures.

Population, fatality, hospitalization, and prevalence statistics are often reported for Na age intervals [ak−1, ak) (k ∈ {1, …, Na}) with . Here, a0 is the smallest age value in the data set and Δaℓ is the width of the ℓ-th age window. We assume that the population size N(ak) is constant in the considered time window. The closed interval [0, 1] contains 0, 1, and all numbers in between, and denotes the set of non-negative integers.