Content
AgeAdjustment
Sometimes, health statistics are used to compare how healthy two different groups of people are, or how healthy a certain group is during two different time periods. Since older people are more likely to get ill, and younger people are more likely to injure themselves, age adjustment can make studies more accurate.
Age is another confounding variable: something that impacts the people being studied but is not related to the health event being studied. To be able to better compare groups while adjusting for age, we use a process called direct standardization.
When we use direct standardization, we assume both groups have the same number of people. Then we calculate the expected number of deaths and death rates in both groups. By doing this, the two populations can be directly compared, independent of the age distribution of each group.
If the agespecific mortality rates (expected deaths) for the population of interest are not known, researchers can use indirect standardization, which requires only the observed deaths and age structure of the population of interest. Direct standardization is generally preferable because the populations of interest are compared to just one standard population, However, indirect standardization can be preferable with small sample sizes in different age groups.
When we use direct standardization, we assume both groups have the same number of people. Then we calculate the expected number of deaths and death rates in both groups. By doing this, the two populations can be directly compared, independent on the age distribution of each group. It is important to remember that age adjusted rates are not the actual rates of death or disease in the population – those are called “crude rates.” Age adjusted rates are only useful for comparisons to other populations.
Expected No. of Deaths in Standardized Populations and AgeAdjusted Death Rates

White 
Black 


Age 
Rate per 1,000 
Population 
Expected no. of deaths 
Rate per 1,000 
Population 
Expected no. of deaths 
<1 yr 
13.3 
15,000 
200 
19.7 
15,000 
295 
14 yr 
0.8 
50,000 
40 
1.7 
50,000 
85 
517 yr 
0.5 
150,000 
75 
0.6 
150,000 
90 
1844 yr 
2.5 
325,000 
800 
3.7 
325,000 
1202.5 
4564 yr 
18.0 
210,000 
3,780 
25.0 
210,000 
5,250 
>65 yr 
70.0 
200,000 
14,000 
77 
200,000 
15,400 
Total 
24.8 
761,000 
18,895 
29.3 
761,000 
22,322.5 
This table shows the expected death rate and number of deaths in a standardized population, which provides the ageadjusted death rates. Ageadjusted rates were calculated by dividing the expected number of deaths by the population (standard) and multiplying by 1,000.
"Population Analysis for Policies and Programmes: Comparison of Direct and Indirect Standardization." http://papp.iussp.org/. United Nations Population Fund (UNFPA), London School of Hygiene and Tropical Medicine and University of London, n.d. Web 5/26/2016