VAT Base Broadening, Self Supply, and the Informal Sector
构建一般均衡模型，分析间接税从窄基（如制造业）向宽基（如增值税）转变的影响，发现税基扩大可能降低福利，因为自我供给和非正规部门活动增加，且非正规部门供给从低收入家庭转向高收入家庭。
We develop a general equilibrium tax model to evaluate the impacts of equal yield base broadening in indirect taxes from high rate narrow based (typically manufactures) taxes to broad based taxes (including services) such as a VAT. We capture differences in choice of mode of supply between market goods, such as manufactures, which cannot be supplied other than through the market, and self-suppliable services and informal sector supplied products. Using this formulation, we are able to provide numerical examples of welfare worsening VAT base broadening, which expands the tax base from market based manufactures, in which there are few (or no) non taxed supply possibilities, to all goods and services where such possibilities exist. We show that the usual presumption that there are welfare benefits from equal yield VAT base broadening breaks down once tax induced increases in self supply of previously non taxed goods and services and in informal sector activity (in small scale construction and other areas) are taken into account. Moreover, since untaxed informal sector supply is typically from lower income to higher income households, they gain as comparable informal sector activity is taxed under the base broadening change. We provide a calibrated version of the model, which captures Canadian base broadening accompanying the introduction of the Canadian VAT (GST) in 1990.