## Definition
^{}

The ratio of the number of events in the population being studied during a certain time period to the estimated population size midway through that time period.

## Comments
^{}

**Guide for use:**

Formula:

R =d/n

Where:

R is the crude rate for the population being studied,

d is the number of events for that population group,

n is the total population for that population group.

**Context:**

Population health and health services research:

Required to calculate population rates, such as incidence rates, prevalence rates, mortality rates and health service utilisation rates.

**Origin:**

Australian Institute of Health and Welfare

**Comments:**

Crude rates are generally multiplied by 1,000 or 100,000 to avoid small decimal fractions. It is then called the crude rate per 1,000 or 100,000 population.

## References

Textbooks of epidemiology, demography and biostatistics.

The presentation of formulae in this data element is based on the notation used in Armitage P & Berry G 1994. *Statistical Methods in Medical Research*. Oxford: Blackwell Scientific Publications.

**See also **Age-standardised rate

This content Based on Australian Institute of Health and Welfare material. Attribution provided as required under the AIHW CC-BY licence.

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