epidemiology Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and determinants of health and disease conditions in a defined population. It is a cornerstone of public health, and shapes policy decisions and evi ...

, a rate ratio, sometimes called an incidence density ratio or incidence rate ratio, is a relative difference measure used to compare the

incidence rate In epidemiology, incidence is a measure of the probability of occurrence of a given medical condition in a population within a specified period of time. Although sometimes loosely expressed simply as the number of new cases during some time p ...

s of events occurring at any given point in time. It is defined as: :

\text = \frac

where incidence rate is the occurrence of an event over person-time (for example person-years): :

\text = \frac

The same time intervals must be used for both incidence rates. A common application for this measure in analytic epidemiologic studies is in the search for a causal association between a certain

risk factor In epidemiology, a risk factor or determinant is a variable associated with an increased risk of disease or infection. Due to a lack of harmonization across disciplines, determinant, in its more widely accepted scientific meaning, is often u ...

and an outcome.

References

Biostatistics Epidemiology Rates {{statistics-stub

See also

References