Department of Health Sciences, Interdisciplinary Graduate School of Medicineand Engineering, University of Yamanashi, Chuo-shi, Yamanashi, Japan.
J Epidemiol Community Health. 2012 Jun;66(6):e11. doi: 10.1136/jech-2011-200321. Epub 2011 Oct 19.
Income inequality has been associated with worse health outcomes in several but not all studies. The heterogeneity across studies may be explained by the variations in the size of area or population over which income inequality was evaluated. Moreover, the studies above a certain inequality threshold, conducted more recently, and incorporating a time lag may have stronger associations between income inequality and health. The authors investigated if the strength of the association between income inequality and health was altered by these factors.
The authors conducted a multivariate meta-regression analysis using nine multilevel cohort studies on income inequality and mortality and 14 multilevel cross-sectional studies on income inequality and self-rated health.
Among cross-sectional studies, studies evaluating country-level inequality (average population>24 million) were more likely to show a stronger association between income inequality and poor health compared with those evaluating income inequality within small average populations (<820 000). There were no significant differences in the effect size of inequality-health association relating to the differences in the population size within a country across which income inequality was evaluated in both cross-sectional and cohort studies. The authors found that the threshold effects, period effects and lag effects were independent of the population size.
Income inequality at the country level may have stronger adverse contextual effects on health than inequality in smaller areas, perhaps by best reflecting social stratification in a society. Furthermore, we found that threshold, period and lag effects were independent of area unit for evaluating inequality, which may have important policy implications.
已有多项研究表明，收入不平等与较差的健康结果有关，但并非所有研究都如此。这些研究之间的异质性可能是由于评估收入不平等的区域或人口规模的差异所导致的。此外，在一定的不平等阈值以上、最近进行的且包含时间滞后的研究，其收入不平等与健康之间的关联可能更强。作者研究了这些因素是否改变了收入不平等与健康之间的关联强度。
作者使用了九项关于收入不平等与死亡率的多层次队列研究和十四项关于收入不平等与自我评估健康的多层次横断面研究，进行了多元荟萃回归分析。
在横断面研究中，评估国家层面不平等（平均人口>2400 万）的研究与评估小平均人口（<82 万）内收入不平等的研究相比，更有可能显示出收入不平等与健康状况不佳之间更强的关联。在横断面和队列研究中，评估收入不平等的国家内的人口规模差异对不平等与健康关联的效应大小没有显著差异。作者发现，阈值效应、时期效应和滞后效应与人口规模无关。
与较小地区的不平等相比，国家层面的收入不平等可能对健康具有更强的不利的背景影响，这可能更好地反映了社会的社会分层。此外，我们发现，阈值、时期和滞后效应与评估不平等的区域单位无关，这可能具有重要的政策意义。
