Denominator data

In epidemiology, data or facts about a population is called denominator data. Denominator data is independent of any specific disease or condition. Disease specific data includes the incidence of disease in a population, the susceptibility of the population to a specific condition, the disease resistance, etc. In mathematical models of disease, disease specific variables often appear in the numerator.

General reference data about the population typically appear in the denominator, hence the term denominator data.

In an epidemiological compartment model, for example, variables are often scaled to total population. The susceptible fraction of a population is obtained by taking the ratio of the number of people susceptible to the total population. Susceptibility to a disease may depend on other factors such as age or sex. Data about a population including age distribution, male/female ratios, and other demographic factors may be relevant as denominator data. Denominator data is not only limited to data describing human populations but also includes information about wild and domestic animal populations.