Long run and short run

In economics, the long run is a theoretical concept in which all markets are in equilibrium, and all prices and quantities have fully adjusted and are in equilibrium. The long run contrasts with the short run, in which there are some constraints and markets are not fully in equilibrium.

More specifically, in microeconomics there are no fixed factors of production in the long run, and there is enough time for adjustment so that there are no constraints preventing changing the output level by changing the capital stock or by entering or leaving an industry. This contrasts with the short run, where some factors are variable (dependent on the quantity produced) and others are fixed (paid once), constraining entry or exit from an industry. In macroeconomics, the long run is the period when the general price level, contractual wage rates, and expectations adjust fully to the state of the economy, in contrast to the short run when these variables may not fully adjust.

History

The differentiation between long-run and short-run economic models did not come into practice until 1890, with Alfred Marshall's publication of his work Principles of Economics. However, there is no hard and fast definition as to what is classified as "long" or "short" and mostly relies on the economic perspective being taken. Marshall's original introduction of long-run and short-run economics reflected the 'long-period method' that was a common analysis used by classical political economists. However, early in the 1930s, dissatisfaction with a variety of the conclusions of Marshall's original theory led to methods of analysis and introduction of equilibrium notions. Classical political economists, neoclassical economists, Keynesian economists all have slightly different interpretations and explanations as to how short-run and long-run equilibria are defined, reached, and what factors influence them.