Lange–Lerner theorem

The Lange model (or Lange–Lerner theorem) is a neoclassical economic model for a hypothetical socialist economy based on public ownership of the means of production and a trial-and-error approach to determining output targets and achieving economic equilibrium and Pareto efficiency. In this model, the state owns non-labor factors of production, and markets allocate final goods and consumer goods. The Lange model states that if all production is performed by a public body such as the state, and there is a functioning price mechanism, this economy will be Pareto-efficient, like a hypothetical market economy under perfect competition. Unlike models of capitalism, the Lange model is based on direct allocation, by directing enterprise managers to set price equal to marginal cost in order to achieve Pareto efficiency. By contrast, in a capitalist economy managers are instructed to maximize profits for private owners, while competitive pressures are relied on to indirectly lower the price to equal marginal cost.

This model was first proposed by Oskar R. Lange in 1936 during the socialist calculation debate, and was expanded by economists like H. D. Dickinson, Abba P. Lerner and Fred M. Taylor. Although Lange and Lerner called it "market socialism", the Lange model is a form of planned economy where a central planning board allocates investment and capital goods, while markets allocate labor and consumer goods. The planning board simulates a market in capital goods by a trial-and-error process first elaborated by Vilfredo Pareto and Léon Walras.

The Lange model has never been implemented anywhere, not even in Oskar Lange's home country, Poland, where Soviet-type economic planning was imposed after World War II, precluding experimentation with Lange-style economy. Some parallels might be drawn with the New Economic Mechanism or so-called Goulash Communism in Hungary under Kádár, although this was not a pure Lange-model system.

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