Incidence and Death Rates
Crude rates are helpful in determining the cancer burden and specific needs for services for a given population, compared with another population, regardless of size. Crude rates are calculated as follows—
- Crude and age-specific incidence rates equal the total number of new cancer cases diagnosed in a specific year in the population category of interest, divided by the at-risk population for that category and multiplied by 100,000 (cancers by primary site) or by 1 million (International Classification of Childhood Cancer [ICCC] groupings of childhood cancers).
- Crude and age-specific death rates equal the total number of cancer deaths during a specific year in the population category of interest, divided by the at-risk population for that category and multiplied by 100,000.
Crude Rates vs. Age-Adjusted Rates
Crude rates are influenced by the underlying age distribution of the state’s population. Even if two states have the same age-adjusted rates, the state with the relatively older population generally will have higher crude rates because incidence or death rates for most cancers increase with increasing age. The age distribution of a population (the number of people in particular age categories) can change over time and can be different in different geographic areas. Age-adjusting the rates ensures that differences in incidence or deaths from one year to another, or between one geographic area and another, are not due to differences in the age distribution of the populations being compared.
2000 U.S. Standard Population Age Groups
The population used to age-adjust the rates in this report is the 2000 U.S. standard population.1 2 In the USCS Data Visualizations tool, the 2000 U.S. standard population is based on the proportion of the 2000 population in 19 specific age groups (younger than 1 year, 1–4 years, 5–9 years, 10–14 years, 15–19 years, … 85 years and older); except for Puerto Rico, where it is based on 18 specific age groups (0–4 years, 5–9 years, 10–14 years, 15–19 years, … 85 years and older); the proportions of the 2000 population in these age groups serve as weights for calculating age-adjusted incidence and death rates. Cancer death rates in the USCS Data Visualizations tool may differ slightly from those published by the National Center for Health Statistics (NCHS) because NCHS uses age groups as recommended by the U.S. Department of Health and Human Services in its adjustment of death rates. In addition, the 2000 U.S. standard population weights are not race- or sex-specific, so they do not adjust for differences in race or sex distribution between geographic areas or populations being compared. They do, however, provide the basis for adjusting for differences in the age distributions across groups defined by sex, race, geography, or other categories.
The 2000 U.S. standard population weights used for this report are based on single years of age from the Census P25-1130 series estimates of the 2000 U.S. population. Populations for single years of age are summed to form the age groups. These standard weights are used to compute age-adjusted incidence and death rates by the method of direct standardization as implemented in the National Cancer Institute’s SEER*Stat software.
Ideally, crude, age-adjusted, and age-specific rates are used to plan for population-based cancer prevention and control interventions.2
- Anderson RN, Rosenberg HM. Report of the Second Workshop on Age Adjustment. Vital and Health Statistics, Series 4 1998;(30):I–VI, 1–37.
- Anderson RN, Rosenberg HM. Age standardization of death rates: implementation of the year 2000 standard. National Vital Statistics Reports 1998;47(3):1–16, 20.