8 C age standardization of mortality rates

real factors

(e.g., environment, healthcare access, behaviors)

CRUDE DEATH RATE

summarizes the overall mortality but does not account for age composition.

It is useful for describing a population internally, but not for comparing between populations.

AGE-SPECIFIC DEATH RATE (ASDR)

Mortality rate within a particular age group.

allow more precise comparisons but can be difficult to use when comparing many populations or age groups.

STANDARDIZED RATES

• These are artificial or adjusted rates that control for age so that two populations can be compared fairly.

Standardization

helps remove the effect of age differences to answer: "If these populations had the same age distribution, would their mortality still differ?"

direct and indirect

2 types of standardization

DIRECT STANDARDIZATION

• Used when:
  = ASDRs are known in the populations being compared.

• We want to compute age-adjusted death rates (ADRs).

INDIRECT STANDARDIZATION

• Used when: ASDRs are not available in the populations of interest.

Only age group structure and total deaths are known.

Populations are small (unstable rates).

standardization mortality ratio (smr)

main output of indirect standardization

SMR = 1.0

→ mortality as expected

SMR > 1.0

→ more deaths than expected

SMR < 1.0

→ fewer deaths than expected

• Age structure differences only

• Real underlying risks (environmental, genetic, occupational, lifestyle)

Standardized mortality helps determine whether differences are due to:

Crude rates

• are simple but misleading for comparison because populations differ in age structure.

Age-specific rates

• provide detail but are hard to compare across many groups.

Age standardization

• allows fair comparison of mortality across populations.

Direct standardization

• uses known ASDRs to compute adjusted death rates.

indirect standardization

uses reference ASDRs to compute SMR when local ASDRs are missing.

Standardized mortality ratios

• (SMRs > 1) indicate higher-than-expected mortality.

Age-adjusted rates and SMRs

• are not real mortality rates, but tools for comparing populations with different age structures.