Definition

In epidemiology

Epidemiology

Epidemiology is the study of health-event, health-characteristic, or health-determinant patterns in a population. It is the cornerstone method of public health research, and helps inform policy decisions and evidence-based medicine by identifying risk factors for disease and targets for preventive...

, data or facts about a population

Population

A population is all the organisms that both belong to the same group or species and live in the same geographical area. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals...

 is called denominator data. Denominator data is independent of any specific disease

Disease

A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...

 or condition. Disease specific data includes the incidence

Incidence (epidemiology)

Incidence is a measure of the risk of developing some new condition within a specified period of time. Although sometimes loosely expressed simply as the number of new cases during some time period, it is better expressed as a proportion or a rate with a denominator.Incidence proportion is the...

 of disease in a population, the susceptibility

Susceptible individual

In epidemiology a susceptible individual is a member of a population who is at risk of becoming infected by a disease, or can not take a certain medicine, antibiotic, etc if he or she is exposed to the infectious agent....

 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

Compartmental models in epidemiology

In order to model the progress of an epidemic in a large population, comprising many different individuals in various fields, the population diversity must be reduced to a few key characteristics which are relevant to the infection under consideration...

, for example, variables are often scaled to total population. The susceptible fraction of a population is obtained by taking the ratio

Ratio

In mathematics, a ratio is a relationship between two numbers of the same kind , usually expressed as "a to b" or a:b, sometimes expressed arithmetically as a dimensionless quotient of the two which explicitly indicates how many times the first number contains the second In mathematics, a ratio is...

 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

Animal

Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...

 populations.

See also

• Incidence
  Incidence (epidemiology)
  Incidence is a measure of the risk of developing some new condition within a specified period of time. Although sometimes loosely expressed simply as the number of new cases during some time period, it is better expressed as a proportion or a rate with a denominator.Incidence proportion is the...
  
  
• Cumulative incidence
  Cumulative incidence
  Cumulative incidence or incidence proportion is a measure of frequency, as in epidemiology, where it is a measure of disease frequency during a period of time...
  
  
• Prevalence
  Prevalence
  In epidemiology, the prevalence of a health-related state in a statistical population is defined as the total number of cases of the risk factor in the population at a given time, or the total number of cases in the population, divided by the number of individuals in the population...
  
  
• Attributable risk
  Attributable risk
  In epidemiology, attributable risk is the difference in rate of a condition between an exposed population and an unexposed population.. Attributable risk is mostly calculated in cohort studies, where individuals are assembled on exposure status and followed over a period of time. Investigators...