This is a secondary research section. The spine of Lewis is the U.S. external position read through the balance of payments and flow of funds (see the current account, who finances the U.S. and the return reversal). The material below is comparison context and a clearly-labeled research extension on unequal exchange / international transfer of value (ITV) — it is not the site's main argument.
Beyond the recorded balance of payments lies a deeper question in international economics: does trade transfer value systematically from poorer to richer countries? The theory of unequal exchange — and the related Prebisch–Singer hypothesis on declining terms of trade for primary producers — argues that it does.[1][2]
Lewis operationalizes this with an International Transfer of Value (ITV) master panel covering 220 economies, applying Köhler's monetary measure of unequal exchange.[3] (The panel also carries 44 World Bank regional and income aggregates, which are not countries and are filtered out of the country lists; 214 of these economies have a full trade profile.) Countries are grouped into a world-system class — core, semi-periphery, periphery — and the panel makes the structural differences visible.
Coverage. The panel's last complete year is 2024. The broad panel — the full economy set and the bulk of the indicators — runs 1960–2024; a narrower historical block (183 economies, nine productivity and factor-share indicators) reaches back to 1950. The stored index runs to 2026, but 2025 and 2026 hold a single U.S. row each on one indicator, so they are partial years and are labelled as such wherever the range appears rather than being read as coverage.
The income gap between the classes is stark and persistent.
Plotting every country's external balance against its income level shows the cross-sectional structure in a single year.