Age-adjusted death rates: consequences of the Year 2000 standard

For nearly 60 years, official U.S. mortality statistics have been age-adjusted using the age distribution from the U.S. population for the year 1940. A new population standard, the projected Year 2000 U.S. standard, has been approved for use by the Department of Health and Human Services (DHHS). It will be implemented for official U.S. Government statistics published for deaths occurring in 1999. The new standard reflects the older age distribution of the population; 6.8% of the population was age 65 years or more in 1940, as compared to 12.6% projected for 2000.

This paper investigates the consequences of the new age distribution standard by comparing death rates by time, place, and population characteristics, adjusted to both the 1940 and projected 2000 population standards.

The new standard changes the level of the age-adjusted death rate for total mortality and for many causes of death, as compared to the 1940 standard. For example, the 1995 death rate for diseases of the heart is 138 per 100,000 population when adjusted using the 1940 standard, but is 296 per 100,000 using the Year 2000 standard. The new standard may change the comparison of age-adjusted rates if there are substantial differences in the age-specific rates. For example, the ratio of age-adjusted death rates for ischemic heart disease in black relative to white males is 1.07 using the 1940 standard, but is 0.96 using the Year 2000 standard.

The new Year 2000 age standard has the potential to change both levels and comparisons of age-adjusted rates. Age-adjustment is an averaging process, and consequently, has the potential to view the data effectively as a whole while possibly obscuring important age-specific details.