Socioeconomic health disparities within and between age groups in the Northern Netherlands
METHODS: Baseline measurements from individuals aged 25-93 years (N=89964) from LifeLines, an observational follow-up study in the Netherlands, were used. Education (8 categories) ranged from no education to academic higher education. Household income (6 categories), standardized for the number of people living in the household, ranged from <€1000 to ≥€2000. Both socioeconomic indicators were also categorized into 3 categories: low; medium; and high. The highest level of education/income served as reference group. SRH was categorized into poor and good. Age was categorized into six groups. Age-stratified logistic regression models adjusted for age and gender were used to examine the association between education/income and SRH using both categorizations.
RESULTS: Using 3 categories, Odds ratios (ORs) for poor SRH were 2.44 ((95% CI) 2.29;2.60) and 2.05 (1.93;2.18) for low education and low income in the overall population. Using 8 and 6 categories, ORs were 4.97 (4.18;5.91) and 2.98 (2.73;3.25) for primary education and an income <€1000. In age-group specific analyses using 8 and 6 categories, ORs were 10.91 (7.07;16.84) and 4.38 (3.52;5.45) for primary education and an income <€1000 in ≥25-≤34 year olds. While ORs for educational level decreased with age to 3.30 (1.39;7.87) in ≥65-≤74 year olds, the ORs for income fluctuated between age groups and was 1.72 (1.22;2.44) in ≥65-≤74 year olds.
CONCLUSIONS: Combining the SES measures education and income obscures variation in the magnitude of socioeconomic gradients in SRH. The magnitude of the socioeconomic gradient in SRH declines with age for educational level and fluctuates for income. A similar obscuring effect holds for combining age-categories.