Premature Mortality by Income Level -- Multnomah County, Oregon, 1976-1984

Health status is difficult to assess because of the heterogeneous nature of populations. To alleviate this problem, officials in Oregon analyzed premature mortality in relation to median household income by census tracts and focused on one racial group. Multnomah County was chosen as the study area because it contains 21% of the state's population and includes Portland, Oregon's largest city. During the study period, 1976-1984, a total of 48,012 white residents of Multnomah County died. These deaths resulted in 303,084 years of potential life lost (YPLL) before 70 years of age.*

Comparative mortality figures (CMF), years of potential life lost indices (YPLLI), and YPLL were calculated for census tracts grouped by median income quintile. The CMF is the ratio of the age-adjusted mortality rate for an income group to the rate for all groups combined. The YPLLI is the ratio of the age-adjusted YPLL rate for an income group to that for all groups. The age adjustment for CMF was calculated by a direct method, and that for YPLLI, by an indirect method (1). In the poorest quintile (Group I) median household income was less than $12,100, and, in the wealthiest quintile (Group V), it was greater than $19,300.

An inverse relationship existed between income levels and the measures of mortality (CMF and YPLLI) due to all causes of death** (Figure 1). For the causes of deaths listed in Table 1, residents of the poorest census tracts (Group I) consistently had the highest mortality, and the wealthiest (Group V) had the lowest. YPLLI differed more between income levels than did CMF. The YPLLI exceeded the CMF by the greatest amount in the lowest income quintile; thus, the greatest excess in premature mortality occurred in this group.

Among the leading causes of death listed in Table 1, the disparity in mortality among income groups is greatest for alcoholism. The YPLLI and CMF decreased in each successive income quintile from Group I to Group V. The YPLLI for alcoholism was 11.7 times higher for Group I than for Group V. Previous studies have shown increased levels of alcohol abuse among persons with low income (4). Others have suggested that alcohol-related diseases are less likely to be reported on the death certificates of persons with higher incomes. The Oregon Center for Health Statistics queries certifying physicians regarding the deaths of any persons for whom the cause of death was suggestive of alcohol abuse (e.g., liver cirrhosis) (5). In 1984, Oregon's mortality rate for all liver disease and cirrhosis (ICD-9 571.0-571.9) was slightly higher (12.0/100,000 population) than that for the United States as a whole (11.6/100,000), but the mortality rate for alcoholic liver disease and cirrhosis (ICD-9 571.0-571.3) was twice as high (9.8 compared with 4.8). In 1984, 82% of all liver disease and deaths from cirrhosis in Oregon were reported to be alcohol-related; this was the highest percentage for any state.

Chronic obstructive pulmonary disease (COPD), the fifth leading cause of death and the ninth leading cause of YPLL, caused the second greatest disparity in mortality among income groups. The YPLLI for COPD was highest for Group I and lowest for Group V; the difference between the two groups was fourfold.

For unintentional injuries, Group I had the highest YPLLI, 1.2 times that of Group V. However, this finding masked a substantial difference in YPLLI for nonmotor vehicle-related unintentional injury (ICD-9 E826-E949); the YPLLI for the poorest quintile was 1.7 times that for the wealthiest. Both groups had similar YPLLI for motor vehicle-related unintentional injuries. Reported by: DD Hopkins, MS, JA Grant-Worley, MS, KL Stebbins, LN Wright, MD, JE Gordon, PhD, LR Foster, MD, State Epidemiologist, Oregon Health Div. Div of Surveillance and Epidemiologic Studies, Epidemiology Program Office, CDC.

Editorial Note

Editorial Note: Years of potential life lost is a measure of mortality that emphasizes causes of death that are important at ages under an arbitrary cut-off, 70 years in this study. A recent study in West Virginia (6) found that crude YPLL rates were higher in counties with low per capita income. The Multnomah County data demonstrate a large variation in premature mortality by economic status in a major metropolitan area. Census tracts are often more homogeneous than counties, and studies based on them may yield a more definitive picture of the relationship between mortality and income. The high rates of premature mortality found in low income areas, in particular, provide direction for public health prevention efforts.

References

1. Kleinman JC. Mortality. In: National Center for Health Statistics. Statistical notes for health planners. No. 3. Rockville, Maryland: US Department of Health, Education, and Welfare, Public Health Service, 1977; PHS publication no. (HRA)77-1237.

2. National Center for Health Statistics. International classification of diseases, adapted for use in the United States. Eighth revision. Washington, DC: US Department of Health, Education, and Welfare, Public Health Service, 1968; PHS publication no. 1693.

3. World Health Organization. Manual of the international statistical classification of diseases, injuries, and causes of death. Ninth revision. Geneva: World Health Organization, 1977.

4. Millar WJ. Sex differentials in mortality by income level in urban Canada. Can J Public Health 1983;74:329-34.

5. Hopkins DD. Questioning the physician: a survey of the cause of death query criteria used by centers for health statistics in the United States and the efficacy of the criteria used by the Oregon Center for Health Statistics. Portland, Oregon: Oregon Department of Human Resources, 1987.

6. Centers for Disease Control. Premature mortality in West Virginia, 1978-1982. MMWR 1987; 36:29-33.

*Seventy years of age was used as the base for YPLL calculations in conformance with recommendations of the National Center for Health Statistics (1). **The International Classification of Diseases (ICD), Eighth Revision Adapted, was used to classify the underlying causes of death during the period 1976-1978 (2). The ICD, Ninth Revision, was used for the period 1979-1984 (3).

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