Epidemiology and Biostatistics, Hunter College, City University of New York, CUNY School of Public Health, New York, NY 10010, USA.
Int J Epidemiol. 2011 Feb;40(1):183-8. doi: 10.1093/ije/dyq189. Epub 2010 Oct 26.
Literature on the socio-economic 'gradient' in health often asserts that income is associated with better health not only for the very poor, but also across the entire income distribution. In addition, changes in the shape of the association between incomes during a period of increasing economic inequality have not been previously studied. The goal of the current study was to estimate and compare the shape of the relationship between income and mortality in the USA for the 1970s, the 1980s and the 1990s.
Using income and mortality data from the Panel Study of Income Dynamics for respondents aged 35-64 years, we used a Bayesian Cox Model with regression splines to model the risk of mortality over three 10-year follow-up periods. To identify whether income was more strongly associated with mortality at different parts of the income distribution, we treated income as a linear spline with an unknown knot location.
The shape of the association between income and mortality was quite non-linear, with a much stronger association at lower levels of income. The relationship between income and mortality in the USA was also not invariant across time, with the increased risk of death associated with lower income applying to an increasing proportion of the US population over time (9th percentile of income in 1970-79, 20th percentile in 1980-89 and 32nd percentile in 1990-99).
Our analyses do not support the claim that income is associated with mortality throughout the income distribution, nor is the association between income and mortality the same across periods. Based on our analyses, a focus on the bottom 30% of the income distribution would seem to return the greatest benefits in reducing socio-economic inequalities in health.
关于健康的社会经济“梯度”的文献通常断言，收入不仅与最贫困人群的健康有关，而且与整个收入分布都有关。此外，在经济不平等程度不断提高的时期，收入之间关联形状的变化尚未得到研究。本研究的目的是估计和比较美国在 20 世纪 70 年代、80 年代和 90 年代期间收入与死亡率之间关系的形状。
使用收入动态面板研究中年龄在 35-64 岁的受访者的收入和死亡率数据，我们使用贝叶斯 Cox 模型和回归样条来对三个 10 年随访期内的死亡率风险进行建模。为了确定收入是否在收入分布的不同部分与死亡率更密切相关，我们将收入视为具有未知结点位置的线性样条。
收入与死亡率之间的关联形状非常非线性，在较低的收入水平下关联更强。美国收入与死亡率之间的关系也不是随时间不变的，随着时间的推移，较低收入与死亡风险增加的关系适用于越来越多的美国人口（1970-79 年的收入 9 分位数，1980-89 年的收入 20 分位数和 1990-99 年的收入 32 分位数）。
我们的分析不支持收入与整个收入分布中的死亡率有关的说法，也不支持收入与死亡率之间的关联在不同时期是相同的。基于我们的分析，关注收入分布的底部 30%似乎可以最大程度地减少健康方面的社会经济不平等。
