The researchers developed a way to measure how domestic policies affect international trade using a Trade Restrictiveness Index. This index shows the equivalent uniform tariff needed to balance out the impact of domestic taxes and subsidies on trade. By incorporating taxes on non-traded goods and factors of production, the index can help predict the effects of policy changes, like agricultural liberalization in Mexico. This approach is based on welfare economics and uses marginal production and consumption shares for accuracy. The Trade Restrictiveness Index offers a consistent way to quantify the trade effects of domestic policies, aiding trade negotiators and policymakers.