1. Class session 6 (AGE) Standardization
Epidemiology 503, Section 2

2. Last Class
We looked at death certificates and mortality rates for stroke
Total (crude) mortality rate
# people who became newly dead (in some time and place) # people in population
Case fatality “rate”
# deaths due to a specific disease
Total # people with that disease

3. Proportional Mortality
Importance of:
Place
Time
Population

5. Age is major contributor to mortality
Specific

6. Thought question
If we want to know: Is a person more likely to die if they were a member of population A as compared to population B? What’s the issue?

7. Even with the same age-specific rates, a population that is younger will appear to have lower overall mortality rates.

8. Why are unadjusted mortality rates problematic?
To Compare Across Populations We Need Comparable Groups

9. Today: Age Standardization
Sweden
Panama
Crude Mortality
Rate
9 per 1000
7 per 1000 10 5 3 15 10 5
Age-Specific Mortality Rates
Old
Old
Middle aged
Middle aged
Young
Young
Adjusted rates allow comparisons of mortality in different populations after removing the confounding effects of age

10. Two Methods Direct Method Indirect Method
Used if age-specific death rates in a population of interest are known
“How would the rates of death compare in 2 populations if they had the same age distribution?”
Indirect Method
Used if age-specific death rates of the population for standardization are unknown or unstable, for example, because the population is small.
“How many deaths would I have expected if this population had the same mortality rates as some standard population?”

11. Rates from Population A Rates from Population B
Because using age-specific death rates from populations typically only used in large groups
For each population:
Calculate age-specific mortality rates
Multiply age-specific rates by the # of people in corresponding age range in standard population
Sum expected # of deaths across age groups
Divide total # of expected deaths by total standard population
Result: Age-adjusted mortality rate for each population of interest
Direct Method
Rates from Population A
Rates from Population B
Applied to
A standard population e.g. US population in 2000 \
Choice of standard is somewhat ARBITRARY.

12. Applied to the age distribution of the study population
Useful when I don’t have or trust the group- specific rates (i.e. population is too small)
Acquire age-specific mortality rates for standard population
Multiply standard population’s age- specific rates by # of people in age range in population of interest
Sum expected # of deaths across age groups in study population
Divide observed # of deaths by expected # of deaths in population of interest
SMR: observed # deaths per year
expected # deaths per year >1 more deaths than expected
=1 as expected <1 less deaths than expected
Indirect Method
Rates from the
standard population
Applied to the age distribution of the study population

13. Example: Same Age-Specific Rates to Populations with Different Ages
Young
0.002
1000
Middle
0.005
500
Old
0.010
200
Total
1700
Rate N
Young
0.002
200
Middle
0.005
500
Old
0.010
1000
Total
1700

14. What are the crude rates?N
Expected Deaths
Young
0.002
1000
1000*0.002 = 2
Middle
0.005
500
500*0.005 = 2.5
Old
0.010
200
200*0.01 = 2
Total
1700
6.5
6.5/1700=0.0038
Rate N
Expected Deaths
Young
0.002
200
200*0.002 = 0.4
Middle
0.005
500
500*0.005 = 2.5
Old
0.010
1000
1000*0.01 = 10
Total
1700
12.9
12.9/1700=0.0076

15. Mathematically It’s a Weighted Average
1700* * *0.01 =
17000
We’re basically just shifting the overall rate to more closely resemble the rates in the groups with the most number of people
Rate N
Young
0.002
1700
Middle
0.005
Old
0.010

16. Decision: Direct or Indirect?
Do you have or are you able to calculate age-specific rates for your population(s) of interest?
Yes  Direct method
No  Indirect method

17. Comparing Standardized Mortality Rates
Direct standardization: Expected rate (or standardized rate) can be compared to the crude rate or to any other similarly standardized rate. Indirect standardization: Expected number of deaths can be compared to the number of actual deaths with the SMR.