Age adjustment
Encyclopedia
In epidemiology
and demography
, age adjustment, also called age standardisation, is a technique used to better allow populations to be compared when the age profiles of the populations are quite different.
For example, in 2004/5, two Australian health surveys investigated rates of long-term circulatory system
health problems (e.g. heart disease) for the general Australian population, and specifically for the Indigenous Australian population. In each age category over age 24, Indigenous Australians had markedly higher rates of circulatory disease than for the general population: 5% vs 2% in age group 25–34, 12% vs 4% in age group 35–44, 22% vs 14% in age group 45–54, and 42% vs 33% in age group 55+.
However, overall, these surveys estimated that 12% of all Indigenous Australians had long-term circulatory problems compared to 18% of the overall Australian population.
To understand this apparent contradiction, note that the Indigenous population is comparatively young (median age 21 years, compared to 37 for non-Indigenous) due to relatively high birth and death rates. Because of this, Indigenous figures are dominated by the younger age groups, which have lower rates of circulatory disease; this masks the fact that their risk is still higher than for non-Indigenous peers of the same age.
In order to get a more informative comparison between the two populations, a weighting
approach is being used. Older groups in the Indigenous population are weighted more heavily (to match their importance in the 'reference population', i.e. the overall Australian population) and younger groups less heavily. This gives an 'age-adjusted' morbidity rate approximately 30% higher than that for the general population, representing the fact that Indigenous Australians do have a higher risk of circulatory disease.
To adjust for age under this direct method of standardization, age-specific rates in each group must be known, as well as the age structure in a standard population.
Age adjustment is commonly used when comparing prevalence
s in different populations; it is also used for characteristics such as life expectancy, average income, and other properties that are not directly linked to the total population size.
Age adjustment is not appropriate when attempting to compare population totals (for instance, if we wanted to know the total number of hospital beds required for patients with circulatory diseases).
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...
and demography
Demography
Demography is the statistical study of human population. It can be a very general science that can be applied to any kind of dynamic human population, that is, one that changes over time or space...
, age adjustment, also called age standardisation, is a technique used to better allow populations to be compared when the age profiles of the populations are quite different.
For example, in 2004/5, two Australian health surveys investigated rates of long-term circulatory system
Circulatory system
The circulatory system is an organ system that passes nutrients , gases, hormones, blood cells, etc...
health problems (e.g. heart disease) for the general Australian population, and specifically for the Indigenous Australian population. In each age category over age 24, Indigenous Australians had markedly higher rates of circulatory disease than for the general population: 5% vs 2% in age group 25–34, 12% vs 4% in age group 35–44, 22% vs 14% in age group 45–54, and 42% vs 33% in age group 55+.
However, overall, these surveys estimated that 12% of all Indigenous Australians had long-term circulatory problems compared to 18% of the overall Australian population.
To understand this apparent contradiction, note that the Indigenous population is comparatively young (median age 21 years, compared to 37 for non-Indigenous) due to relatively high birth and death rates. Because of this, Indigenous figures are dominated by the younger age groups, which have lower rates of circulatory disease; this masks the fact that their risk is still higher than for non-Indigenous peers of the same age.
In order to get a more informative comparison between the two populations, a weighting
Weighting
The process of weighting involves emphasizing the contribution of some aspects of a phenomenon to a final effect or result — giving them 'more weight' in the analysis. That is, rather than each variable in the data contributing equally to the final result, some data are adjusted to contribute...
approach is being used. Older groups in the Indigenous population are weighted more heavily (to match their importance in the 'reference population', i.e. the overall Australian population) and younger groups less heavily. This gives an 'age-adjusted' morbidity rate approximately 30% higher than that for the general population, representing the fact that Indigenous Australians do have a higher risk of circulatory disease.
To adjust for age under this direct method of standardization, age-specific rates in each group must be known, as well as the age structure in a standard population.
Age adjustment is commonly used when comparing 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...
s in different populations; it is also used for characteristics such as life expectancy, average income, and other properties that are not directly linked to the total population size.
Age adjustment is not appropriate when attempting to compare population totals (for instance, if we wanted to know the total number of hospital beds required for patients with circulatory diseases).