In economics, the Prebisch–Singer hypothesis (also called the Prebisch–Singer thesis) argues that the price of primarycommodities 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. , recent statistical studies have given moderate support for the idea. The idea was initially developed by Hans Singer in 1948–49 and expanded by Raúl Prebisch shortly thereafter; since that time, it has served as a major pillar of dependency theory and policies such as import substitution industrialization (ISI).