In
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 evide ...
, 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 peri ...
s of events occurring at any given point in time.
It is defined as:
:
where incidence rate is the occurrence of an event over person-time (for example
person-years):
:
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 use ...
and an outcome.
See also
*
Odds ratio
An odds ratio (OR) is a statistic that quantifies the strength of the association between two events, A and B. The odds ratio is defined as the ratio of the odds of A in the presence of B and the odds of A in the absence of B, or equivalently (due ...
*
Ratio
In mathematics, a ratio shows how many times one number contains another. For example, if there are eight oranges and six lemons in a bowl of fruit, then the ratio of oranges to lemons is eight to six (that is, 8:6, which is equivalent to the ...
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Risk ratio
References
Biostatistics
Epidemiology
Rates
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