03 Age standardization

Question 1

Why is age standardisation important?

Answer 1

• allows comparison of diseases in two areas with different ages
  
  • age is often a determinating factor for disease

Question 2

Name the two main methods for age standardisation

Answer 2

• direct standardisation (ASR)
  
  • absolute measure of risk
• indirect standardisation (SIR)

Question 3

How to calculate the ASR?

Answer 3

1. calculate age-specific incidence (Cases / population size in area) -> risk
2. multiply the risk with a fitting standard population (same for both areas) -> expected values
3. sum up the expected values per area -> total ASR

Question 4

Important for direct standardisation

Answer 4

• same standard population for all populations that are compared
• standard population should by close to original population structure

Question 5

How to calculate the SIR?

Answer 5

SIR is an estimate and relative measure when no age was recorded

1. take the risk per age from a reference and multiply it with your population of that age (risk (reference) x population) -> expected cases per age
2. sum up the expected cases per age -> total expected cases
3. compare the total expected cases with your total observed cases (observed / expected = SIR) to get the SIR

Question 6

Important for indirect standardisation (SIR)

Answer 6

• only total case number and age structure needed
• relative estimate
  
  • < 1 reduced risk compared to ref.
  • = 1 equal risk compared to ref.
  • > 1 higher risk compared to ref.