Incidence of Hypertension and Educational Attainment The NHANES I Epidemiologic Followup Study

Clemencia M. Vargas, Deborah D. Ingram and Richard F. Gillum

From the Office of Analysis, Epidemiology, and Health Promotion, National Center for Health Statistics, Centers for Disease Control and Prevention, Hyattsville, MD.


    ABSTRACT
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Previous research has demonstrated the association between cardiovascular disease and education. However, few studies have described the incidence of hypertension, a risk factor for cardiovascular disease, by education or other socioeconomic status indicators. To examine the association between hypertension incidence and education, the authors analyzed data from the First National Health and Nutrition Examination Survey (NHANES I) Epidemiologic Followup Study (NHEFS) (1971–1984). The relative risk of hypertension incidence (blood pressure >= 160/95 and/or using antihypertensive medication) by education was calculated for non-Hispanic Whites (aged 25–64 years) and non-Hispanic Blacks (aged 25–44 years) normotensive at baseline using Cox proportional hazards models. The age-adjusted relative risk of hypertension incidence among persons with less than 12 years of education compared with those with more than 12 years was significant among non-Hispanic Whites aged 25–44 years (men: relative risk (RR) = 2.14, 95% confidence interval (CI): 1.29, 3.54; women: RR = 2.06, 95% CI: 1.39, 3.05) but not among non-Hispanic Blacks (RR = 1.16, 95% CI: 0.63, 2.14). Relative risks for non-Hispanic White men remained stable after adjusting for age, systolic blood pressure, body mass index, and region of residence; relative risks for non-Hispanic White women were reduced but remained significant. Non-Hispanic White men and women aged 45–64 years with less than 12 years of education were not at higher risk of developing hypertension compared with their more educated counterparts. These results demonstrate a significant interaction between age and education with an independent association between education and hypertension incidence among younger but not older non-Hispanic White men and women. Am J Epidemiol 2000;152:272–8.

education; hypertension; nutrition surveys; social class

Abbreviations: CI, confidence interval; NHANES I, First National Health and Nutrition Examination Survey; NHEFS, NHANES I Epidemiologic Followup Study; RR, relative risk.


    INTRODUCTION
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Cardiovascular disease is the leading cause of death in the United States (1Go). The negative association of cardiovascular disease morbidity and mortality with socioeconomic status has been demonstrated by several studies (2GoGoGoGoGoGoGoGo–10Go). These studies have shown that individuals with lower socioeconomic status, as measured by education and/or occupation, are more likely to have cardiovascular disease than are individuals with higher socioeconomic status. Even though hypertension is one of the main risk factors for cardiovascular disease, a review of the literature shows few studies of hypertension incidence (11GoGoGoGo–15Go) and even fewer studies of the association between hypertension incidence and education or other indicators of socioeconomic status (16GoGoGoGo–20Go). A study of Blacks in Charleston, South Carolina, found that hypertension incidence was inversely associated with social class as measured by education and occupation (16Go, 18Go); another study of inner city Blacks found that hypertension incidence was associated with income but not with education or occupation (17Go). The First National Health and Nutrition Examination Survey (NHANES I) Epidemiologic Followup Study (NHEFS) is the only longitudinal nationally representative survey of the US population that permits the analysis of hypertension incidence by sociodemographic characteristics. Waitzman and Smith (20Go) and Ford and Cooper (19Go) used the NHEFS to study the incidence of hypertension. Waitzman and Smith (20Go) analyzed the incidence of hypertension among men by occupational mobility; they found that hypertension incidence was higher among men who were from lower occupational classes or those who moved to lower occupational classes than among their counterparts. Ford and Cooper (19Go) studied the relation between incidence of hypertension and several sociodemographic, behavioral, and biochemical factors among persons 25 years of age and over. They found a significant bivariate association between the incidence of hypertension and educational attainment among White men, White women, and Black women. After controlling for diverse covariates, this association remained significant only among White women. In this study we use data from the NHEFS to extend these findings by exploring how the association of educational attainment and incidence of hypertension among men and women varies with age and other possible effect modifiers.


    MATERIALS AND METHODS
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Study population
The NHANES I collected data in 1971–1975 on a nationwide, multistage, probability sample of the civilian non-institutionalized US population aged 1–74 years, excluding Alaska, Hawaii, and reservation lands of American Indians. Details of the plan, complex survey design, response rates, and operation were published previously (21Go). The elderly, women of child-bearing age, and persons living in poverty areas were oversampled. Data were collected through personal interview, physical examination, and laboratory analyses. The NHEFS is a longitudinal study of participants in the NHANES I who were 25–74 years of age at the time of the survey examination in 1971–1975 (22Go). The personal interviews and physical and laboratory examinations of the NHANES I provided the baseline data for the NHEFS. This analysis is based on the first wave of follow-up during 1982–1984, because this was the only wave that included blood pressure measurements.

This analysis includes non-Hispanic White persons who were 25–64 years of age at baseline and non-Hispanic Black persons who were 25–44 years of age. Persons from racial/ethnic groups other than non-Hispanic White and non-Hispanic Black were excluded because sample sizes were too small to make separate estimates. Elderly persons (65 years of age and over) were not included in the analysis, because almost half of the elderly persons who were normotensive at baseline died before the 1982–1984 follow-up and these deaths were concentrated in the lowest education group. Thus, the inclusion of elderly persons would bias the results toward the null. Finally, non-Hispanic Blacks 45–64 years of age were also excluded because their sample size is too small to provide reliable estimates.

Of the 9,840 non-Hispanic White persons aged 25–64 years and non-Hispanic Black persons aged 25–44 years at baseline, we excluded from analysis 808 (5.6 percent) who were lost to follow-up, 500 (3.5 percent) who died before the 1982–1984 follow-up, and 59 (0.4 percent) who were traced but not interviewed in 1982–1984. Also excluded from the analyses were women who were pregnant at baseline or follow-up (n = 104), persons with unknown baseline or follow-up blood pressure measurements or antihypertensive medication use (n = 1,110), persons with unknown educational attainment (n = 160), and persons who were hypertensive at baseline (n = 1,261), that is, had systolic blood pressure equal to or greater than 160 mmHg, had diastolic blood pressure equal to or greater than 95 mmHg, and/or reported using antihypertensive medication. After all exclusions, 5,861 persons with normal blood pressure (1,976 non-Hispanic White men, 3,413 non-Hispanic White women, and 472 non-Hispanic Black men and women) remained for analysis. Included and excluded persons with normal blood pressure, for whom data were available, had overall similar mean systolic blood pressure (p = 0.28) and similar mean body mass index (p = 0.06); excluded persons with normal blood pressure were more likely to have lower educational attainment (p = 0.001) and to be younger (p = 0.001) than persons included in the study.

Outcome variable
Incident hypertension was defined as follow-up systolic blood pressure equal to or greater than 160 mmHg and/or diastolic blood pressure equal to or greater than 95 mmHg and/or follow-up report of current use of antihypertensive medication. This definition of hypertension was chosen because it was the clinical definition of hypertension in use at the time of the baseline and follow-up examinations. The date of the follow-up examination in 1982–1984 was considered the date of incidence because it is not possible to identify the actual date of onset.

Measurement of variables
At the baseline physical examination, blood pressure measurements were taken at a mobile examination center by a physician with the participant seated. One blood pressure measurement was attempted for all participants; two additional blood pressure measurements were attempted for a subsample of participants. Approximately 30 percent of the blood pressure measurements were taken with an aneroid sphygmomanometer, and the remainder were taken with a standard mercury sphygmomanometer. There were no significant differences in blood pressure by type of sphygmomanometer used (23Go). Two cuff sizes, pediatric and adult, were available. The cuff most appropriate for the participant's arm circumference was placed over the bulge in the upper right arm. Diastolic blood pressure was measured at the point of complete cessation of Korotkoff's sounds or, if there was no cessation, the point of muffling. Measurements were recorded to the nearest 2 mm on the scale (23Go).

At follow-up, blood pressure was measured three times in the participant's home by a trained interviewer. These measurements were taken at the end of the interview with the participant seated using a mercury sphygmomanometer. Three cuffs (pediatric, adult, and large) were available (22Go). Similar results were obtained when using all available blood pressure measurements or only the first measurement; therefore, for consistency, only the first measurement at baseline and follow-up is used for these analyses.

Educational attainment at baseline was measured as the highest completed grade of school and categorized as less than 12 years, 12 years, and more than 12 years. Self-reported race and ethnicity as obtained at follow-up were used in the analyses (22Go). Poverty status is defined by the ratio of family income to the federal poverty line threshold that is established annually by the US Bureau of the Census and adjusted by family composition. For this analysis, poverty status was defined as less than 100 percent of the federal poverty level, from 100 to less than 200 percent of the federal poverty level, and 200 percent and above. Multiple dichotomous variables (Northeast, Midwest, West, and South as the reference category) were used to represent region of residence to account for regional variation in hypertension prevalence and socioeconomic status.

Statistical methods
Demographic and other characteristics of the participants were compared. Hypertension incidence rates were calculated as the number of incident cases per 1,000 person-years at risk. Estimates of the risk of developing hypertension among persons with less than 12 years and 12 years of education relative to those with more than 12 years of education were derived from Cox proportional hazards models using the PHREG procedure in the Statistical Analysis System (24Go). Cox proportional hazards models account for the difference in follow-up time among participants, which ranged from 6.7 to 12.6 years (mean 5 9.9 years). Persons who did not develop hypertension were censored at the date of the follow-up examination.

All models included age at baseline, in single years, as a covariate. Risk-adjusted models also included baseline body mass index (kg/m2), region of residence, and systolic blood pressure (mmHg). Systolic blood pressure is included to control for borderline or labile blood pressure elevations at baseline.

Separate analyses were performed for non-Hispanic White men, non-Hispanic White women, and non-Hispanic Blacks because of the well-known racial/ethnic and sex differentials in the prevalence of hypertension (25Go). Sex-specific analyses were not performed for non-Hispanic Blacks because of small sample size. Models for non-Hispanic Blacks also included sex as a covariate. Interactions among baseline education, age, body mass index, region of residence, and systolic blood pressure were examined for each racial/ethnic-sex group.

The association between hypertension incidence and education was examined for nonlinearity by performing analyses with education entered in the model as a continuous variable together with the square of education (not shown). No evidence of nonlinearity was found for non-Hispanic White men, non-Hispanic White women, or non-Hispanic Blacks. We checked the proportional hazards assumption by plotting the log-log survival curves for the education subgroups and by testing time-dependent covariates for education. The log-log survival curves were approximately parallel, and the time-dependent covariates were not significant, so we concluded that the data fit the proportional hazards assumption.

To assess the effect of the complex survey design on the results, the proportional hazard models were also run using PROC SURVIVAL in SUDAAN (26Go). The results were consistent with minimal effects of the complex survey design on the main conclusions derived from the unweighted estimates. Therefore, the estimates from the unweighted Cox regression models are presented (27Go).


    RESULTS
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Table 1 presents the means or percentages of baseline risk factors by racial/ethnic group, sex, and education in the analysis cohort. Persons with less than 12 years of education were older than persons with more education. Overall, the mean systolic blood pressure tended to be higher in the less than 12 years of education group than in the more than 12 years of education group. The differential was statistically significant only among younger non-Hispanic White women. Non-Hispanic White women with less than 12 years of education had a significantly higher mean body mass index than their counterparts with more education.


View this table:
[in this window]
[in a new window]
 
TABLE 1. Demographic and other characteristics at baseline* among normotensive participants by racial/ethnic group and educational attainment, NHEFS,{dagger} 1971–1984

 
Table 2 presents the number of incident hypertension cases by racial/ethnic group, sex, baseline age, and education. There were 919 incident cases of hypertension during the follow-up period. For non-Hispanic Whites, the incidence rate of hypertension per 1,000 person-years, also shown in table 2, was consistently higher among middle-aged persons than among younger persons. For all demographic groups, the hypertension incidence rate tended to be higher among persons with less than 12 years of education than among those with more than 12 years of education. However, the 95 percent confidence intervals indicate that the differences in the incidence rate by education were statistically significant only among non-Hispanic White men and women 25–44 years of age.


View this table:
[in this window]
[in a new window]
 
TABLE 2. Number of incident cases of hypertension and incidence rate by racial/ethnic group, sex, baseline age, and education in the analysis cohort, NHEFS,* 1971–1984

 
The proportional hazard models indicated the presence of a significant interaction between education and age among non-Hispanic White men and non-Hispanic White women 25–64 years of age (p < 0.001) but not among non-Hispanic Black persons 25–44 years of age; there was also a significant interaction between body mass index and systolic blood pressure among non-Hispanic White women 25–44 years of age. There were no other significant interactions. Therefore, the models for non-Hispanic White persons were run separately for younger persons (25–44 years) and middle-aged persons (45–64 years), and risk-adjusted models for younger non-Hispanic White women included the interaction term, body mass index x systolic blood pressure.

The age-adjusted risk of hypertension incidence was significantly higher among younger non-Hispanic White men and women with less than 12 years of education compared with those with more than 12 years (men: relative risk (RR) = 2.14, 95 percent confience interval (CI): 1.29, 3.54; women: RR = 2.06, 95 percent CI: 1.39, 3.05) (table 3). The relative risk of hypertension for non-Hispanic White men changed little after adjusting for baseline risk factors (RR = 2.01, 95 percent CI: 1.21, 3.35); the relative risk for women was reduced but it was still significant (RR = 1.50, 95 percent CI: 1.002, 2.236). The risk of hypertension incidence for persons with less than 12 years of education compared with those with more than 12 years of education was not significant in middle-aged non-Hispanic White men and women or in younger non-Hispanic Blacks.


View this table:
[in this window]
[in a new window]
 
TABLE 3. Relative risk of hypertension incidence associated with education in White persons and Black persons, NHEFS,{dagger} 1971–1984

 
A proportional hazards model with education included as a continuous variable was run for non-Hispanic Blacks to explore whether the categorization of education may be masking the association between education and hypertension incidence. No significant association was found between hypertension incidence and single years of educational attainment (RR = 0.97, 95 percent CI: 0.93, 1.02). To account for the lower educational attainment among older persons and non-Hispanic Blacks (table 1), we also performed analyses with education categorized as 0–7, 8–11, and 12 and more years of educational attainment. No association was found between hypertension incidence and these education categories in non-Hispanic Whites aged 45–64 years or in non-Hispanic Blacks (not shown).

Poverty status was also included in the models to explore the possible effects of socioeconomic status not represented by educational attainment. We chose poverty status over family income because the data on income provided by the NHANES I are in uneven categories and are truncated at $25,000, which makes them unsuitable for multivariate analyses. Poverty status was significantly associated with the incidence of hypertension only among older non-Hispanic women; the association between educational attainment and the incidence of hypertension remained almost unchanged after adding poverty status to the models. A study of the incidence of hypertension and occupational class also found poverty not significant (20Go). To maintain the models in their more parsimonious form, poverty status was not included in the final models.


    DISCUSSION
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
In this study we examined the prospective relation between educational attainment and subsequent hypertension among non-Hispanic White men and women aged 25–64 years and non-Hispanic Black men and women aged 25–44 years from a nationally representative sample. Educational attainment was selected as the main socioeconomic status variable because it has been reported as the facet of socioeconomic status more determinant of health status, particularly cardiovascular conditions (28Go), it is the variable that structures occupation and income (29Go), and it is the only indicator that remains relatively consistent through adult life (5Go). We found a previously unreported interaction between baseline age and education that was highly significant (p < 0.001). The risk of developing hypertension after adjusting for age is inversely associated with educational attainment among non-Hispanic White persons 25–44 years of age at baseline; non-Hispanic White men and women in this age group with less than 12 years of education have a higher risk of hypertension than their counterparts with more than 12 years of education. The association of education and risk of developing hypertension among non-Hispanic White men 25–44 years of age could not be explained by the risk factors included in the models, body mass index, region of residence, and systolic blood pressure; among non-Hispanic White women 25–44 years of age, these risk factors explained part of the association between education and the risk of developing hypertension. However, no association was found in non-Hispanic Whites aged 45–64 years.

The lack of difference in the risk of hypertension among persons 45–64 years of age could have been a cohort effect associated with the overall increase of education in the US population (30Go), which could result in a different meaning of educational attainment for each age group; that is, the disadvantages of not finishing high school were greater for the younger group than for the older one. To explore this possibility, we performed the analysis with educational attainment classified as 0–8, 9–11, and 12 and over (data not shown); the relative risk estimates among persons 45–64 years of age using these new categories of education were essentially the same as those obtained using the original categorization.

Although the association between hypertension incidence and educational attainment in non-Hispanic Blacks 25–44 years of age failed to achieve statistical significance and was reduced after controlling for age (table 2), two previous studies have reported an association between hypertension incidence and socioeconomic status among Blacks. A 14-year follow-up study in Charleston, South Carolina, found a negative association between hypertension incidence and an index based on education and occupation among Blacks (16Go, 18Go). This study included a group of high socioeconomic status non-Hispanic Blacks to increase the socioeconomic status variation of the study sample. A 3-year follow-up study of non-Hispanic Blacks residing in the inner city of Baltimore, Maryland, found an association between hypertension incidence and income but not between hypertension incidence and education (analyses performed using multiple regression with a binary dependent variable) (17Go). In models with poverty status instead of education, we did not find that poverty was associated significantly with hypertension incidence. The lack of association in our study may be due in part to the small number of non-Hispanic Blacks in the NHEFS with more than 12 years of education, which yielded only 13 cases (table 2). Hence, the statistical power of our analysis was low; confidence intervals indicate that an important association cannot be excluded. When the analysis was repeated using the education categories 0–8, 9–11, and 12 years and over, no significant association was found.

A previous analysis of NHEFS studying the association between the incidence of hypertension and multiple sociodemographic and behavioral variables found a significant association between education and hypertension incidence in White women 25–74 years of age at baseline (p < 0.000) and a borderline association in White men (p = 0.055) after controlling for multiple risk factors (19Go). However, this study did not control for the strong interaction between education and age that exists among non-Hispanic White persons in the NHEFS as shown by our analyses. Our age group-specific analyses indicated that education is associated with the risk of hypertension only among younger non-Hispanic White persons but not among persons 45–64 years of age.

The finding that younger non-Hispanic White men and women with lower educational attainment are more likely to become hypertensive than their counterparts with higher educational attainment may reflect the deleterious effects of lower socioeconomic conditions of life on health. Studies have shown that persons living in lower socioeconomic status environments are more exposed to health insults, some of which are associated with hypertension: depression (31Go), sedentarism (32Go, 33Go), and behaviors to cope with life's hardships such as alcohol intake (33Go, 34Go) and cigarette smoking (33Go). Our results indicating an association of hypertension incidence and educational attainment only among the younger group are consistent with the "weathering" hypothesis proposed by Geronimus (35Go, 36Go). This hypothesis contends that persons living in low socioeconomic status conditions see their health profiles worsening at earlier ages than their counterparts living in more favorable conditions (36Go). In our study, middle-aged persons with low education who survive the younger years without hypertension are at the same risk as their counterparts with more education.

Limitations of this analysis include possible bias arising from loss to follow-up, missing data on baseline risk variables, and missing data at follow-up. In addition, participants who died between baseline and follow-up could not be included in the analysis. This situation may produce a bias because most persons who died or were lost to follow-up were in the low education group and the older age group. This bias was reduced by limiting the analyses to participants 25–64 years of age. Another limitation is that the use of only one blood pressure measurement may introduce errors due to within-person blood pressure variability. Although analyses including all available measurements were consistent with those presented here, some misclassification bias associated with within-person blood pressure variability may remain. Unfortunately, the NHEFS does not provide repeated blood pressure measurements at follow-up to correct for within-person measurement error (37Go, 38Go). However, there is no reason to believe that this possible bias is associated with educational attainment; thus, any bias of results on incidence of hypertension by educational attainment should be toward the null. Bias in the model coefficients could also be caused by substantial intraindividual variation in one of the independent variables, baseline systolic blood pressure (and also systolic blood pressure x body mass index in the case of younger White women). This could occur independent of the likelihood of misclassification of the outcome variable. Assuming that baseline systolic blood pressure is positively associated with incident hypertension and that educational attainment is negatively associated with baseline systolic blood pressure, the bias is likely toward the null, but bias away from the null cannot be excluded. The small number of non-Hispanic Black men and women precluded more detailed analysis by sex and age groups and caused a lack of precision as reflected by wide confidence intervals, so that a significant association of risk of hypertension with educational attainment could not be excluded. The possibility of confounding by variables not measured cannot be excluded.

In summary, our results confirm previous findings that persons with low educational attainment are at higher risk of hypertension; they add to previous reports the finding that the excess risk of hypertension for non-Hispanic White persons with low education is confined to early adulthood, 25–44 years of age. Non-Hispanic White men and women 25–44 years of age with lower educational attainment are at higher risk of hypertension than their counterparts with higher educational attainment, even after adjusting for risk factors. No association between educational attainment and risk of hypertension was found for middle-aged non-Hispanic White participants. Our results of no association between education and the incidence of hypertension among non-Hispanic Black participants 25–44 years of age should be considered with caution because of the small sample size. Future studies should assess this association using population samples including larger numbers of non-Hispanic Blacks, as well as persons from other racial/ethnic groups, and the elderly.


    ACKNOWLEDGMENTS
 
The NHANES I Epidemiologic Followup Study has been developed and funded by these agencies: National Center for Health Statistics; National Institute on Aging; National Cancer Institute; National Institute of Child Health and Human Development; National Heart, Lung, and Blood Institute; National Institute of Mental Health; National Institute of Diabetes and Digestive and Kidney Diseases; National Institute of Arthritis and Musculoskeletal and Skin Diseases; National Institute of Allergy and Infectious Diseases; National Institute of Neurological and Communicative Disorders and Stroke; Centers for Disease Control and Prevention; and the US Department of Agriculture. The field work was conducted by Westat, Inc. (contract nos. 233-80-2049 and 282-84-2111).


    NOTES
 
Reprint requests to Dr. Clemencia M. Vargas, Office of Analysis, Epidemiology, and Health Promotion, National Center for Health Statistics, CDC, 6525 Belcrest Road, Room 730, Hyattsville, MD 20782 (e-mail: cav5{at}cdc.gov).

This paper was presented during the 4th International Conference on Preventive Cardiology, June 1997, Montreal, Canada.


    REFERENCES
 TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

  1. Ventura SJ, Peters KD, Martin JA, et al. Births and deaths: United States, 1996. Mon Vital Stat Rep 1997;46(1 suppl 2):1–40.
  2. Kraus JF, Borhani NO, Franti CE. Socioeconomic status, ethnicity, and risk of coronary heart disease. Am J Epidemiol 1980;111:407–14.[Abstract]
  3. Rose G, Marmot MG. Social class and coronary heart disease. Br Heart J 1981;45:13–19.[Abstract]
  4. Marmot MG, Shipley MJ, Rose G. Inequalities in death: specific explanations of a general pattern? Lancet 1984;1:1003–6.[ISI][Medline]
  5. Feldman JJ, Makuc DM, Kleinman JC, et al. National trends in educational differentials in mortality. Am J Epidemiol 1989;129:919–33.[Abstract]
  6. Tyroler HA. Socioeconomic status in the epidemiology and treatment of hypertension. Hypertension 1989;13(suppl I):I94–7.[Medline]
  7. Modan B, Wagener DK. Some epidemiological aspects of stroke: mortality/morbidity trends, age, sex, race, socioeconomic status. Stroke 1992;23:1230–6.[Abstract]
  8. Luepker RV, Rosamond WD, Murphy R, et al. Socioeconomic status and coronary heart disease risk factor trends. The Minnesota Heart Study. Circulation 1993;88(part 1):2172–9.
  9. Howard G, Russell GB, Anderson R, et al. Role of social class in excess black stroke mortality. Stroke 1995;26:1759–63.[Abstract/Free Full Text]
  10. Casper ML, Barnett EB, Armstrong DL, et al. Social class and race disparities in premature stroke mortality among men in North Carolina. Ann Epidemiol 1997;7:46–53.[ISI][Medline]
  11. Apostolides AY, Cutter G, Daugherty SA, et al. Three-year incidence of hypertension in thirteen US communities. On behalf of the Hypertension Detection and Follow-up Program Cooperative Group. Prev Med 1982;11:487–99.[ISI][Medline]
  12. Rabkin SW, Mathewson FAL, Tate RB. Relationship of blood pressure in 20-39-year-old men to subsequent blood pressure and incidence of hypertension over a 30-year observation period. Circulation 1982;65:291–300.[Abstract]
  13. Dannenberg AL, Garrison RJ, Kannel WB. Incidence of hypertension in the Framingham Study. Am J Public Health 1988;78:676–9.[Abstract]
  14. Gillum RF, Mussolino ME. White blood cell count and hypertension incidence. The NHANES I Epidemiologic Follow-up Study. J Clin Epidemiol 1994;47:911–19.[ISI][Medline]
  15. Shetterly SM, Rewers M, Hamman RF, et al. Patterns and predictors of hypertension incidence among Hispanics and non-Hispanic whites: the San Luis Valley Diabetes Study. J Hypertens 1994;12:1095–102.[ISI][Medline]
  16. Keil JE, Tyroler HA, Sandifer SH, et al. Hypertension: effects of social class and racial admixture. The results of a cohort study in the black population of Charleston, South Carolina. Am J Public Health 1977;67:634–9.[Abstract]
  17. Dischinger PC, Apostolides AY, Entwisle G, et al. Hypertension incidence in an inner-city black population. J Chronic Dis 1981;34:405–13.[ISI][Medline]
  18. Keil JE, Sandifer SH, Loadholt CB, et al. Skin color and education effects on blood pressure. Am J Public Health 1981;71:532–4.[Abstract]
  19. Ford ES, Cooper RS. Risk factors for hypertension in a national cohort study. Hypertension 1991;18:598–606.[Abstract]
  20. Waitzman NJ, Smith KR. The effects of occupational class transitions on hypertension: racial disparities among working-age men. Am J Public Health 1994;84:945–50.[Abstract]
  21. Miller HW. Plan and operation of the Health and Nutrition Examination Survey. United States–1971–1973. Vital Health Stat 1 1973;10a:1–46. (DHEW publication no. (PHS) 79-1310).
  22. Cohen BB, Barbano HE, Cox CS, et al. Plan and operation of the NHANES I Epidemiologic Followup Study: 1982–84. Vital Health Stat 1 1987;22:1–142. (DHHS publication no. (PHS) 87-1324).[Medline]
  23. Roberts J, Maurer K. Blood pressure levels of persons 6–74 years. United States, 1971–1974. Vital Health Stat 11 1977;203:i–v, 1–103. (DHEW publication no. (HRA) 78-1648).
  24. SAS Institute, Inc. SAS/STAT software: changes and enhancements, release 6.07. Cary, NC: SAS Institute, Inc, 1992:433–80. (SAS technical report P-229).
  25. Burt VL, Whelton P, Roccella EJ, et al. Prevalence of hypertension in the adult US population: results from the Third National Health and Nutrition Examination Survey, 1988–1991. Hypertension 1995;25:305–13.[Abstract/Free Full Text]
  26. Shah BV, Barnwell BG, Bieler GS. SUDAAN user's manual: software for analysis of correlated data, release 6.40. Research Triangle Park, NC: Research Triangle Institute, 1995.
  27. Ingram DD, Makuc DM. Statistical issues in analyzing the NHANES I Epidemiologic Followup Study. Vital Health Stat 2 1994;121:1–30. (DHHS publication no. (PHS) 94-1395).[Medline]
  28. Winkleby MA, Jatalius DE, Frank E, et al. Socioeconomic status and health: how education, income, and occupation contribute to risk factors for cardiovascular disease. Am J Public Health 1992;82:816–20.[Abstract]
  29. Ross CE, Wu C. The links between education and health. Am Sociol Rev 1995;60:719–45.[ISI]
  30. Mare RD. Changes in educational attainment and school enrollment. In: Farley R, ed. State of the Union: America in the 1990s. New York, NY: Russell Sage Foundation, 1995.
  31. Jonas BS, Wilson RW. Negative mood and urban versus rural residence: using proximity to metropolitan statistical areas as an alternative measure of residence. Adv Data 1997;281:1–12. (DHHS publication no. (PHS) 97-1250).[Medline]
  32. Ford ES, Merritt RK, Heath GW, et al. Physical activity behaviors in lower and higher socioeconomic status populations. Am J Epidemiol 1991;133:1246–56.[Abstract]
  33. Pamuk ER, Makuc DM, Heck KE, et al. Socioeconomic status and health chartbook. Health, United States, 1998. Hyattsville, MD: National Center for Health Statistics, 1998.
  34. Midanik LT, Klatsky AL, Armstrong MA. Changes in drinking behavior: demographic, psychosocial, and biomedical factors. Int J Addict 1990;25:599–619.[ISI][Medline]
  35. Geronimus AT. Black/white differences in the relationship of maternal age to birthweight: a population-based test of the weathering hypothesis. Soc Sci Med 1996;42:589–97.[ISI][Medline]
  36. Geronimus AT. The weathering hypothesis and the health of African-American women and infants: evidence and speculations. Ethn Dis 1992;2:207–21.[Medline]
  37. Rosner BA, Spiegelman D, Willett WC. Correction of logistic regression relative risk estimates and confidence intervals for random within-person measurement error. Am J Epidemiol 1992;136:1400–13.[Abstract]
  38. Rosner BA, Cook NR. Screening rules for determining blood pressure status in clinical trials. Application to the trials of hypertension prevention. Am J Epidemiol 1993;137:1341–52.[Abstract]
Received for publication September 16, 1999. Accepted for publication November 4, 1999.