Optimal Tax Design and Enforcement with an Informal Sector
比较了贸易税与增值税在部分商品由非正规部门生产时的优劣，发现增值税能实现正规部门的生产效率但无法间接对利润征税，而政府通过高成本执法改变非正规部门规模可能使增值税更优。
An optimal commodity tax approach is taken to compare trade taxes and VATs when some commodities are produced informally. Trade taxes apply to all imports and exports, including intermediate goods, while the VAT applies only to sales by the formal sector and imports. The VAT achieves production efficiency within the formal sector, but, unlike trade taxes, cannot indirectly tax profits. Making the size of the informal sector endogenous in each regime is potentially decisive. The ability of the government to change the size of the informal sector through costly enforcement may also tip the balance in favor of the VAT.