### Description

Age standardisation is a process of adjusting for a population's rate of injury to account for changes in the age structure of the population over time. Age standardised rates provide an estimate of an individual's average annual risk of being injured. Age standardisation adjusts the rates of injury to account for changes in the age structure of a population over time. It allows comparison of the rates of injury from one year to another, taking into account the ageing population.

For example, you can calculate rates for person-years at risk if you have 50 cases of injury diagnosed over two years and a starting population of 200,000. The incidence rate per 100,000 is (50 / (200,000 x 2 years)) x 100,000 = 12.5 cases per 100,000 people over two years. Note that 400,000 is the number of person-years at risk, which is calculated by multiplying the starting population by the number of years.

To calculate the incidence rate for one year, you divide your rate by the number of years observed. So, for the example above, the number of cases for one year is ((50 / (200,000 x 2)) x 100,000) / 2 = 6.25 per ‘100,000 person-years at risk’ for one year.

The ‘at risk’ subset of the population means everyone in each specified sex, ethnicity, and age range who is potentially at risk of the relevant injury. For example, rates of falls for those aged 75 and over (75+) are only calculated based on people aged 75+ in the population.

Age-standardised rates per 100,000 person-years at risk is an internationally recognised, and internationally comparable standard for reporting injury statistics rates.