Most health insurance uses cost-sharing to reduce excess utilization. Supplemental insurance can blunt the impact of this cost-sharing, increasing utilization and exerting a negative externality on the primary insurer. This paper estimates the effect of private Medigap supplemental insurance on public Medicare spending using Medigap premium discontinuities in local medical markets that span state boundaries. Using administrative data on the universe of Medicare beneficiaries, we estimate that Medigap increases an individual's Medicare spending by 22.2 percent. We calculate that a 15 percent tax on Medigap premiums generates savings of $12.9 billion annually with a standard error of $4.9 billion.

中文翻译：

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补充保险的外部性和税收：Medicare 和 Medigap 的研究

大多数健康保险使用成本分摊来减少过度使用。补充保险可以减弱这种成本分摊的影响，提高利用率并对主要保险公司施加负面外部性。本文使用跨越州界的当地医疗市场中的 Medigap 保费不连续性来估计私人 Medigap 补充保险对公共医疗保险支出的影响。使用关于医疗保险受益人范围的行政数据，我们估计 Medigap 将个人的医疗保险支出增加了 22.2%。我们计算出对 Medigap 保费征收 15% 的税后，每年可节省 129 亿美元，标准误差为 49 亿美元。