消費外部性、自我保險與最適租稅政策

Consumption Externality, Self-Insurance, and Optimal Taxation

本文建構了一個包含消費外部性的個人自我保險模型，文中有二項主要的發現。第一，當個人偏好為妒忌 (jealousy) 且為風險趨避時，個人均衡的自我保險投入會低於社會的最適水準，此一結果明顯異於Dupor and Liu (2003) 的論點。第二， 當個人均衡屬於低度（過度）自我保險時，假若政府資金的邊際成本 (marginal cost of public funds, MCPF) 等於1，則政府可透過對個人的損失課稅（扣除），或者對其自我保險投入補貼（課稅）來矯正此一扭曲。然而，當政府資金的邊際成本大於1 時，假若個人均衡屬於低度自我保險時，則政府應對個人的損失課稅；反之，當個人均衡屬於過度自我保險時，則應對個人從事自我保險的投入課稅。

This paper constructs a self-insurance model in the presence of consumption externality. We have two major findings. First, if an individual is jealous and risk averse, then the equilibrium level of self-insurance will be lower than the social optimum. This result is significantly different from that of Dupor and Liu (2003). Second, when the marginal cost of public funds (MCPF) equals one, the government should tax (subsidize) losses or subsidize (tax) self-insurance if consumers are under- (over-) insured. However, when the MCPF is greater than one, the government should tax losses if consumers are under-insured and tax self-insurance if consumers are over-insured.