We compared all-cause mortality rates stratified by individual-level education and by census tract area–based socioeconomic measures for Massachusetts (1999–2001). Among persons aged 25 and older, the age-adjusted relative index of inequality was slightly higher for the census tract than for the individual education measures (1.5 vs 1.2, respectively). Only the census tract socioeconomic measures could provide a relative index of inequality (2–3) for deaths before age 25 or detect expected socioeconomic disparities for deaths among persons 65 and older (relative index of inequality= approximately 1.2 vs 0.8 for census tract measures and individual education, respectively).
Population health data stratified by socioeconomic position are critical for monitoring and analyzing health disparities. When individual-level socioeconomic measures are not available, as is often the case with health surveillance data,1–4 an alternative approach is to use census tract area–based socioeconomic measures to characterize rates in relation to the socioeconomic position of the immediate areas in which people reside.1,3–6 Moreover, even when individual-level education data are available (e.g., for death certificates), the public-release census summary files before the 2000 US census did not provide data on educational level cross-tabulated by age, needed for denominators. In this study, we used the newly available 2000 census population counts for education level cross-tabulated by age to report and compare, for the first time, the socioeconomic inequalities in mortality detected with individual-level education data and census tract area–based socioeconomic measures.
METHODSWe obtained mortality data, including years of individual education,7 from the state of Massachusetts for the years 1999 to 2001 (N = 165 217) and geocoded all deceased persons according to the address on the death certificate. We employed a commercial geocoding firm with known high accuracy8; thus, we were able to geocode 97% of the records with certainty to the census tract level. A priori determined categories for individual-level education and the 3 census tract area–based socioeconomic measures (percentage of persons below poverty, percentage of adults aged 25 and older with less than a high-school education, and percentage of adults aged 25 and older with a 4-year college education) are shown in Tables 1 ▶ and 2 ▶.3,4
TABLE 1—Age-Standardized All-Cause Mortality Rates, by Individual-Level Education and Census Tract Area–Based Socioeconomic Measures: Adults Aged 25 and Older, Massachusetts, 1999–2001
Deaths Person-Yearsa Age-Standardized Mortality Rates,b per 100 000 Incident Rate Ratio (95% CI) Relative Index of Inequality(95% CI) Individual level: education, y 1.23 (1.21, 1.26) ≥16 22 897 4255 870 1.00 12–15 103 182 6612 1507 1.73 (1.71, 1.76) < 12 33 340 1954 1016 1.17 (1.15, 1.19) Census tract level Percentage below poverty 1.46 (1.44, 1.49) 0.0–4.9 60 356 5416 1096 1.00 5.0–9.9 48 999 3866 1185 1.08 (1.06, 1.10) 10.0–19.9 30 098 2140 1390 1.27 (1.25, 1.29) 20.0–100 18 175 1379 1453 1.33 (1.29, 1.37) Percentage adults 25 and older with less than a high-school education 1.53 (1.51, 1.57) 0.0–14.9 88 589 7857 1107 1.00 15.0–24.9 38 415 2844 1301 1.18 (1.16, 1.21) 25.0–39.9 21 683 1502 1451 1.31 (1.29, 1.34) 40.0–100 8941 606 1472 1.33 (1.31, 1.35) Percentage adults 25 and older with a bachelor’s degree 1.45 (1.43, 1.48) 40.0–100 41 315 3908 1061 1.00 25.0–39.9 44 963 3744 1172 1.10 (1.08, 1.13) 15.0–24.9 40 619 3040 1276 1.20 (1.18, 1.22) 0.0–14.9 30 731 2117 1435 1.35 (1.33, 1.37) TABLE 2—Age-Stratified All-Cause Mortality Rates, by Individual-Level Education and Census Tract Area–Based Socioeconomic Measures: Massachusetts, 1999–2001
Deaths Person-Yearsa Age-Stratified Mortality Rates, per 100 000 Incident Rate Ratio (95% CI) Relative Index of Inequality (95% CI) Ages 0–24 y Individual-level education, y . . . ≥16 . . . . . . . . . . . . 12–15 . . . . . . . . . . . . < 12 . . . . . . . . . . . . Census tract–level percentage below poverty 2.33 (2.03, 2.67) 0.0–4.9 800 2490 32 1.00 5.0–9.9 729 1636 45 1.38 (1.25, 1.53) 10.0–19.9 544 1080 50 1.57 (1.41, 1.75) 20.0–100 615 1032 60 1.86 (1.67, 2.06) Census tract–level percentage of adults 25 and older with less than a high-school education 2.93 (2.55, 3.38) 0.0–14.9 1201 3614 33 1.00 15.0–24.9 639 1131 49 1.46 (1.33, 1.61) 25.0–39.9 561 894 63 1.89 (1.71, 2.09) 40.0–100 287 418 69 2.06 (1.81, 2.35) Census tract–level percentage of adults 25 and older with a bachelor’s degree 3.03 (2.64, 3.48) 40.0–100 496 1852 27 1.00 25.0–39.9 662 1656 40 1.46 (1.33, 1.61) 15.0–24.9 716 1440 50 1.89 (1.71, 2.09) 0.0–14.9 814 1290 63 2.06 (1.81, 2.35) Ages 25–44 y Individual-level education, y 6.75 (6.12, 7.45) ≥16 1061 2321 46 1.00 12–15 4723 3066 154 3.37 (3.15, 3.60) < 12 1074 603 178 3.90 (3.58, 4.24) Census tract–level percentage below poverty 3.34 (3.06, 3.65) 0.0–4.9 1855 2364 78 1.00 5.0–9.9 1875 1779 105 1.34 (1.26, 1.43) 10.0–19.9 1559 1073 145 1.85 (1.73, 1.98) 20.0–100 1482 748 198 2.52 (2.36, 2.70) Census tract–level percentage of adults 25 and older with less than a high-school education 3.72 (3.41, 4.07) 0.0–14.9 2969 3545 84 1.00 15.0–24.9 1738 1363 127 1.52 (1.44, 1.62) 25.0–39.9 1369 753 181 2.17 (2.04, 2.32) 40.0–100 695 309 225 2.69 (2.48, 2.92) Census tract–level percentage of adults 25 and older with a bachelor’s degree 3.63 (3.32, 3.96) 40.0–100 1231 1794 69 1.00 25.0–39.9 1735 1721 101 1.52 (1.44, 1.62) 15.0–24.9 1835 1408 130 2.17 (2.04, 2.32) 0.0–14.9 1970 1047 188 2.69 (2.48, 2.92) Ages 45–64 y Individual-level education, y 2.79 (2.65, 2.94) ≥16 4356 1478 295 1.00 12–15 14 508 2189 662 2.25 (2.17, 2.33) < 12 3316 586 566 1.92 (1.84, 2.01) Census tract–level percentage below poverty 2.81 (2.67, 2.94) 0.0–4.9 7722 1980 390 1.00 5.0–9.9 6461 1259 513 1.31 (1.27, 1.36) 10.0–19.9 4300 632 680 1.74 (1.68, 1.81) 20.0–100 3441 385 894 2.29 (2.20, 2.38) Census tract–level percentage of adults 25 and older with less than a high-school education 2.91 (2.77, 3.06) 0.0–14.9 11 354 2745 413 1.00 15.0–24.9 5497 889 619 1.50 (1.45, 1.54) 25.0–39.9 3504 451 776 1.88 (1.81, 1.95) 40.0–100 1569 174 900 2.18 (2.06, 2.29) Census tract–level percentage of adults 25 and older with a bachelor’s degree 2.68 (2.55, 2.81) 40.0–100 4899 1354 361 1.00 25.0–39.9 6078 1267 480 1.50 (1.45, 1.54) 15.0–24.9 5820 998 583 1.88 (1.81, 1.95) 0.0–14.9 5127 640 801 2.18 (2.06, 2.29) Ages ‡65 y Individual-level education, y 0.80 (0.78, 0.81) ≥16 17 480 457 3829 1.00 12–15 83 951 1357 6185 1.62 (1.59, 1.64) < 12 28 950 765 3784 0.99 (0.97, 1.01) Census tract–level percentage below poverty 1.23 (1.21, 1.26) 0.0–4.9 50 779 1072 4736 1.00 5.0–9.9 40 663 828 4911 1.04 (1.02, 1.05) 10.0–19.9 24 239 435 5572 1.18 (1.16, 1.20) 20.0–100 13 252 246 5387 1.14 (1.12, 1.16) Census tract–level percentage of adults 25 and older with less than a high-school education 1.29 (1.27, 1.32) 0.0–14.9 74 266 1567 4740 1.00 15.0–24.9 31 180 592 5268 1.11 (1.10, 1.13) 25.0–39.9 16 810 298 5632 1.19 (1.17, 1.21) 40.0–100 6677 123 5418 1.14 (1.11, 1.17) Census tract–level percentage of adults 25 and older with a bachelor’s degree 1.24 (1.22, 1.27) 40.0–100 35 185 760 4630 1.00 25.0–39.9 37 150 756 4914 1.11 (1.10, 1.13) 15.0–24.9 32 964 634 5195 1.19 (1.17, 1.21) 0.0–14.9 23 634 430 5492 1.14 (1.11, 1.17)To calculate age-standardized rates for the population aged 25 and older (Table 1 ▶), we used the US year 2000 standard million for ages 25 and older.9 We used the least deprived group as the comparison group to calculate incidence rate ratios for individual-level education and census tract area–based socioeconomic measures. We could not compute mortality rates by individual-level education for individuals younger than 25 because persons in this age group may not have completed their education, and the requisite person-year data for denominators were not available for persons younger than 18.10 On the basis of age-standardized rates, we calculated the relative index of inequality, which is a coefficient of linear slope that takes into account the effect estimate of each socioeconomic category weighted by the number of individuals in that category.11–13 This measure permits meaningful comparison of health inequalities across diverse socioeconomic measures, even if their proportionate allocation of persons across socioeconomic strata differs.
RESULTSTable 1 ▶ presents data on deaths, person-years, and age-standardized mortality rates for the population aged 25 and older, by individual-level education and by census tract area–based socioeconomic measure. Table 2 ▶ presents the same data for 4 age strata (0–24, 25–44, 45–64, ≥ 65). The individual-level education and census tract area–based socioeconomic measures had a similar low proportion of missing data (typically less than 3%).
For the population aged 25 and older (Table 1 ▶), the degree of socioeconomic inequality in mortality detected with the census tract area–based socioeconomic measures was slightly greater than that detected by the individual-level education measure (relative index of inequality of approximately 1.5 vs 1.2). Additionally, as shown in Table 2 ▶, only the census tract area–based socioeconomic measures yielded estimates of socioeconomic inequality for persons younger than 25 (relative index of inequality between 2.3 and 3.0). For persons aged 25 to 44, the magnitude of the relative index of inequality was greater for the individual-level education measure (6.8) compared with the census tract area–based socioeconomic measures (range = 3.3–3.7) but was similar for persons aged 45 to 64 (range = 2.7–2.9). For persons aged 65 and older, the relative index of inequality was significantly below 1 for individual-level education (0.8) but ranged between 1.2 and 1.3 for the 3 census tract area–based socioeconomic measures.
DISCUSSIONOur findings suggest that census tract area–based socioeconomic measures such as “percentage of persons below poverty” and individual-level education detect a similar magnitude of socioeconomic inequality for all-cause mortality in the state of Massachusetts for individuals between ages 45 and 64. Census tract area–based socioeconomic measures also uniquely provide evidence of socioeconomic inequality for (1) persons younger than 25 years, for whom education may not yet be completed; and (2) persons aged 65 and older, for whom individual-level education analyses indicated that mortality rates were higher among persons with 12 to 15 years of education than among those with both less than 12 and 16 or more years. However, for persons aged 25 to 44, the magnitude of the relative index of inequality for the census tract area–based socioeconomic measures, although still large (approximately 3.5), was less than that yielded by the individual-level education (6.8).
Consistent with our results, previous empirical research has reported selective misclassification in education level on death certificates, chiefly because of individuals who did not graduate from high school being reported as having obtained a high-school diploma, especially among persons aged 65 and older.15,16 The net effect is to deflate the mortality rate among persons with fewer than 12 years of education and inflate it among persons with 12 to 15 years of education.15 For this reason, the National Center for Health Statistics report Socioeconomic Status and Health provided mortality rates by individual education only for individuals between ages 25 and 64.16 Importantly, studies with self-reported individual-level educational data document socioeconomic inequality in all-cause mortality analogous to that detected with this study’s census tract area–based socioeconomic measures.17
Census tract area–based socioeconomic measures thus offer 2 advantages over individual-level education data for monitoring socioeconomic inequality in mortality. First, they provide an estimate of effect with decreased misclassification bias for persons aged 65 and older. Second, they can be used validly for persons younger than 25.
Of note, our use of census tract area–based socioeconomic measures is unlikely to be substantially affected by ecological bias, given the similar direction of estimates for the individual and area-based socioeconomic measures and results that are of a comparable magnitude (except for older ages, for which individual data are likely misclassified). From an etiological standpoint, multilevel analyses assessing the relative contribution of individual- and area-level socioeconomic characteristics to social inequities in mortality would be useful.18–21 Future research also should evaluate whether our findings vary by type of mortality,22 race/ethnicity, and gender.
AcknowledgmentsThis work was funded by the National Institutes of Health (grant 1 R01 HD3685-01) via the National Institute of Child Health and Human Development and the Office of Behavioral and Social Science Research (Principal Investigator, Nancy Krieger). S. V. Subramanian is supported by the National Institutes of Health Career Development Award (1 K25 HL081275 )
We thank Bruce Cohen (Division of Research and Epidemiology, Massachusetts Department of Public Health) for facilitating the conduct of this study with data from the Massachusetts Health Department and for providing helpful comments. We also thank Malena Orejuela Hood (Division of Research and Epidemiology, Massachusetts Department of Public Health) and Charlene Zion (Registry of Vital Records and Statistics, Massachusetts Department of Public Health) for assistance with data handling and preparation.
Human Participant Protection Use of the data in this study was approved by all relevant institutional review boards and human subjects committees at the Harvard School of Public Health and the Massachusetts Department of Public Health.
Peer Reviewed
Contributors D. H. Rehkopf led the data analysis and writing. L. T. Haughton assisted with data analysis and manuscript preparation. J. T. Chen developed the tools for data analysis and assisted with data analysis. P.D. Waterman assisted with data preparation. S. V. Subramanian assisted with data interpretation. N. Krieger originated the study and assisted with manuscript preparation. All authors helped to conceptualize ideas, interpret findings, and review drafts of the manuscripts.
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