Socioeconomic status and survival after stroke - using mediation and sensitivity analyses to assess the effect of stroke severity and unmeasured confounding
Socioeconomic status and survival after stroke - using mediation and sensitivity analyses to assess the effect of stroke severity and unmeasured confounding
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DOI：
10.1186/s12889-020-08629-1
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发表时间：
2020-04-25
影响因子：
4.5
通讯作者：
Eriksson, Marie
中科院分区：
文献类型：
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作者：
Lindmark, Anita;Norrving, Bo;Eriksson, Marie
背景虽然已经证实低社会经济地位与卒中后死亡风险的增加有关，但这种联系背后的机制仍然不清楚。在这项研究中，我们旨在通过调查卒中严重程度的差异在多大程度上解释卒中后存活率的差异来阐明收入水平与卒中后存活率的关系。方法研究基于2009-2012年瑞典卒中登记的首次缺血性卒中(n=51,159)或脑出血(n=6777)的患者。我们使用因果中介分析将低收入对3个月病死率的影响分解为中风严重程度的直接影响和间接影响。由于因果中介分析依赖于关于相关关系剩余混淆的强有力的假设，最近开发的敏感性分析方法被用来评估结果对未观察到的混淆的稳健性。结果调整了观察到的混杂因素后，收入最低的三分位数的患者与收入最高的两个三分位数的患者相比，脑出血后3个月死亡的绝对风险增加了3.2%(95%可信区间：0.9-5.4%)。缺血性卒中后病死率相应增加1%(0.4-1.5%)。低收入对脑出血的间接效应为1.8%(0.7-2.9%)，对缺血性中风的间接效应为0.4%(0.2-0.6%)。未观察到的混杂因素影响低收入、更严重的中风和病例死亡的风险的方向相同，可以解释间接影响，但对观察到的混杂因素的额外调整不会改变结论。结论本研究提供了证据，在与收入相关的卒中病例死亡率中，多达一半是通过卒中严重程度的差异来调节的。因此，以卒中严重程度为目标可以大幅减少不平等，应该优先考虑。敏感性分析表明，需要对比年龄影响更大的混杂因素进行额外调整，才能显著改变我们的结论。
BackgroundAlthough it has been established that low socioeconomic status is linked to increased risk of death after stroke, the mechanisms behind this link are still unclear. In this study we aim to shed light on the relationship between income level and survival after stroke by investigating the extent to which differences in stroke severity account for differences in survival.MethodsThe study was based on patients registered in Riksstroke (the Swedish stroke register) with first time ischemic stroke (n=51,159) or intracerebral hemorrhage (n=6777) in 2009-2012. We used causal mediation analysis to decompose the effect of low income on 3-month case fatality into a direct effect and an indirect effect due to stroke severity. Since causal mediation analysis relies on strong assumptions regarding residual confounding of the relationships involved, recently developed methods for sensitivity analysis were used to assess the robustness of the results to unobserved confounding.ResultsAfter adjustment for observed confounders, patients in the lowest income tertile had a 3.2% (95% CI: 0.9-5.4%) increased absolute risk of 3-month case fatality after intracerebral hemorrhage compared to patients in the two highest tertiles. The corresponding increase for case fatality after ischemic stroke was 1% (0.4-1.5%). The indirect effect of low income, mediated by stroke severity, was 1.8% (0.7-2.9%) for intracerebral hemorrhage and 0.4% (0.2-0.6%) for ischemic stroke. Unobserved confounders affecting the risk of low income, more severe stroke and case fatality in the same directions could explain the indirect effect, but additional adjustment to observed confounders did not alter the conclusions.ConclusionsThis study provides evidence that as much as half of income-related inequalities in stroke case fatality is mediated through differences in stroke severity. Targeting stroke severity could therefore lead to a substantial reduction in inequalities and should be prioritized. Sensitivity analysis suggests that additional adjustment for a confounder of greater impact than age would be required to considerably alter our conclusions.