Does Self-Rated Health Mean the Same Thing Across Socioeconomic Groups? Evidence From Biomarker Data
Introduction
Self-rated health (SRH) status on a five-point scale has been used extensively in the study of health inequalities by socioeconomic status (SES), based partly on its ease of collection and consistent associations with subsequent morbidity and mortality 1, 2, 3. Concerns have arisen, however, that the measurement of health inequalities with SRH may be biased if individuals from different socioeconomic groups have systematically different expectations or reporting standards for health, sometimes called “reporting heterogeneity” 4, 5. Recently, other investigators have examined whether equivalent SRH translates into the same “objective” health status across different socioeconomic groups by testing whether the association of SRH with mortality risk varies by SES. Results have been mixed; SRH was a stronger predictor of mortality for higher SES groups in the United States and the Netherlands, a weaker predictor for higher SES groups in France, and an equal predictor across SES in Sweden and the United Kingdom 6, 7, 8, 9, 10, 11, 12. Several investigators also have found evidence for reporting heterogeneity by SES by using alternative benchmarks for “objective” health such as self-reported clinical illnesses or physical functioning 13, 14, or the more detailed self-reported MacMaster Health Utility Index and SF-36 instrument 4, 15.
Profiles of biological risk present a promising “objective” benchmark for SRH with several advantages over mortality risk or other self-reported measures such as functional limitations or chronic conditions. The use of self-reported conditions or functional limitations as a benchmark for SRH cannot rule out reporting heterogeneity that may be shared by both sets of self-reports. The use of clinical or physician-reported illness as a benchmark also suffers from potential biases resulting from differential access to care and probability of diagnoses. Biomarkers, in contrast, are measured in the laboratory and avoid this type of systematic reporting error. Although a few researchers have investigated the relation of biomarkers to SRH 16, 17, 18, only one study to our knowledge has tested whether levels of biomarkers across SRH categories vary by SES. In the United Kingdom, average measures of body mass index (BMI) and blood pressure across two categories of SRH were found to differ between manual versus nonmanual worker categories for women but not for men (19).
We aimed to expand upon this work by analyzing a broader array of biomarkers and a wider range of SRH and SES categories in a large, nationally representative U.S. sample. We tested whether levels of important markers of metabolic, cardiovascular, and inflammatory risk and organ functioning vary by education for adults reporting the same category of SRH. These results will contribute evidence to the nature of reporting differences in SRH and improve our understanding of the strengths and potential biases of SRH as a measure of population health.
Section snippets
Methods
Data are from the Third National Health and Nutrition Examination Survey (NHANES III), conducted by the U.S. National Center for Health Statistics between 1988 and 1994. NHANES III is a cross-sectional stratified multistage probability sample of the civilian noninstitutionalized U.S. population age 2 months to 90 years. Data were collected in household interviews, clinical examinations, and laboratory tests. Details of the sampling design and protocol have been previously reported 20, 21.
We
Results
Descriptive statistics for the sample are shown in Table 1. A total of 21% of respondents reported “excellent” health, 30.4% “very good,” 32.3% “good,” 13.0% “fair,” and 3.3% “poor.” Mean levels of biomarkers across four categories of SRH are shown separately in Table 2 for men and women. For almost all markers, mean levels differed significantly across SRH categories in the expected direction. Those reporting worse health had greater levels of systolic and diastolic BP, BMI, waist-hip ratio,
Discussion
Using data from a nationally representative U.S. sample, we identified differences in biological risk within SRH categories by education, especially for higher levels of SRH. These results provide evidence that a given level of SRH may not translate into the same objective health for different SES groups and suggest that researchers should use caution in interpreting differences in SRH by SES.
Strengths of this study include the use of a large, nationally representative sample of the
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