The economic models developed in the 1920s and 1930s by American economists Fred M. Taylor and Abba Lerner and by Polish economist Oskar R. Lange involved a form of planning based on marginal cost pricing. In Lange's model, a central planning board would set prices for producer goods through a trial-and-error method, adjusting until the price matched the marginal cost, with the aim of achieving Pareto-efficient outcomes. Although these models were often described as market socialism, they actually represented a form of market simulation planning.