Very low birth weight hospital volume and mortality: an instrumental variables approach.
Very low birth weight hospital volume and mortality: an instrumental variables approach.
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极低出生体重住院人数和死亡率：工具变量方法。
DOI：
10.1097/mlr.0b013e31824e32cf
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发表时间：
2012
期刊：
影响因子：
3
通讯作者：
Xie,Yang
中科院分区：
文献类型：
--
作者：
Wehby,GeorgeL;Ullrich,Fred;Xie,Yang
背景：先前关于极低出生体重（VLBW）医院容积对住院死亡率影响的研究使用了标准的风险调整模型，该模型仅考虑可观察混杂因素，而不考虑由不可观察混杂因素引起的自我选择偏倚。目的：利用工具变量（IV）模型，在明确考虑不可观察混杂因素和自我选择偏倚的情况下，评估VLBW婴儿住院容量对住院死亡率的影响。方法：选取2000-2004年在新泽西州63家医院出生的VLBW婴儿4553例为研究对象。我们使用IV分析，将患者与最近的低容量医院（每年< 50名VLBW婴儿）、中等容量医院（每年51-100名VLBW婴儿）和高容量医院（每年100名VLBW婴儿）之间的距离作为工具。我们评估了几个体积测量，并根据可观察到的婴儿和医院特征进行了调整。结果：我们发现，在经典的风险调整模型中，有益的体积对生存的影响被显著低估，在该模型中，与高体积相比，低体积和中等体积分别使死亡率增加1.8倍和1.88倍（风险比分别为1.4和1.5）。然而，使用IV方法，我们发现低和中等容量分别使死亡率增加5.42倍和3.51倍（风险比分别为2.76和2.21）。这些发现表明，不可观察的混杂因素增加了选择死亡率更高的婴儿进入规模较大的医院。结论：考虑到未观察到的自我选择偏倚，在大容量医院分娩和治疗VLBW婴儿可以获得很大的生存益处。这支持了在大医院为极低生育能力妇女提供分娩和高危妊娠护理的区域化政策。
Background:Previous studies of very low birth weight (VLBW) hospital volume effects on in-hospital mortality have used standard risk-adjusted models that only account for observable confounders but not for self-selection bias due to unobservable confounders.Objective:To assess the effects of hospital volume of VLBW infants on in-hospital mortality while explicitly accounting for unobservable confounders and self-selection bias using an instrumental variables (IV) model.Methods:The sample includes 4553 VLBW infants born in 63 hospitals in 2000–2004 in New Jersey. We use IV analysis with the differences between the patient’s distances to the nearest low (< 50 VLBW infants annually), moderate (51–100 infants annually), and high (> 100 VLBW infants annually)-volume hospitals as instruments. We evaluate several volume measures and adjusted for observable infant and hospital characteristics.Results:We find beneficial volume effects on survival that are significantly underestimated in classic risk-adjusted models, under which low and moderate volumes compared with high volumes increase mortality odds by 1.8 and 1.88 times, respectively (risk ratios of 1.4 and 1.5, respectively). However, using the IV approach, we find that low and moderate volumes increase mortality odds by 5.42 and 3.51 times, respectively (risk ratios of 2.76 and 2.21, respectively). These findings suggest unobservable confounders that increase the selection of infants at a greater mortality risk into higher-volume hospitals.Conclusions:Accounting for unobserved self-selection bias reveals large survival benefits from delivering and treating VLBW infants at high-volume hospitals. This supports policies regionalizing the delivery and care for pregnancies at risk for VLBW at high-volume hospitals.