Prebisch–Singer hypothesis
In economics, the Prebisch–Singer hypothesis (also called the Prebisch–Singer thesis) argues that the price of primary commodities declines relative to the price of manufactured goods over the long term, which causes the terms of trade of primary-product-based economies to deteriorate. As of 2013, recent statistical studies have given support for the idea.
Source: Wikipedia — Prebisch–Singer hypothesis (CC BY-SA 4.0)