Individuals that consume different baskets of goods are differentially affected by relative price changes caused by international trade. We develop a methodology to measure the unequal gains from trade across consumers within countries that is applicable across countries and time. The approach uses data on aggregate expenditures across goods with different income elasticities and parameters estimated from a non-homothetic gravity equation. We find considerable variation in the pro-poor bias of trade depending on the income elasticity of each country’s exports and imports. Non-homotheticities across sectors imply that trade typically favors the poor, who concentrate spending in more traded sectors. (Emphasis added.)
So trade helps the poor given the fact that the poor concentrate their spending in the traded sectors of the economy. Fajgelbaum and Khandelwal writes,
We also find important effects from sectoral heterogeneity. As in the single-sector setting, the pro-poor bias increases with a country’s income elasticity of exports. But, in contrast with the single-sector estimation, the multi-sector model implies a strong pro-poor bias of trade in every country. On average over the countries in our sample, the real income loss from closing off trade are 57 percent for the 10th percentile of the income distribution and 25 percent for the 90th percentile.5 This bias in the gains from trade toward poor consumers hinges on the fact that these consumers spend relatively more on sectors that are more traded, while high-income individuals consume relatively more services, which are the least traded sector. Additionally, low-income consumers happen to concentrate spending on sectors with a lower elasticity of substitution across source countries. As a result, the multi-sector setting implies larger expenditures in more tradeable sectors and a lower rate of substitution between imports and domestic goods for poor consumers; these two features lead to larger gains from trade for the poor than the rich.