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In microeconomics, the long run is the conceptual time period in which there are no fixed factors of production, so that there are no constraints preventing changing the output level by changing the capital stock or by entering or leaving an industry. The long run contrasts with the short run, in which some factors are variable and others are fixed, 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.〔Paul A. Samuelson and William D. Nordhaus (2004). ''Economics'', 18th ed., () Glossary of Terms, "Long run" and "Short run."〕 ==Long run== In the long run, firms change production levels in response to (expected) economic profits or losses, and the land, labor, capital goods and entrepreneurship vary to reach associated long-run average cost. In the simplified case of plant capacity as the only fixed factor, a generic firm can make these changes in the long run: * enter an industry in response to (expected) profits * leave an industry in response to losses * increase its plant in response to profits * decrease its plant in response to losses. The long run is associated with the long-run average cost (LRAC) curve in microeconomic models along which a firm would minimize its average cost (cost per unit) for each respective long-run quantity of output. ''Long-run marginal cost'' (''LRMC'') is the added cost of providing an additional unit of service or commodity from changing capacity level to reach the lowest cost associated with that extra output. LRMC equalling price is efficient as to resource allocation in the long run. The concept of ''long-run cost'' is also used in determining whether the long-run expected to induce the firm to remain in the industry or shut down production there. In long-run equilibrium of an industry in which perfect competition prevails, the LRMC = LRAC at the minimum LRAC and associated output. The shape of the long-run marginal and average costs curves is determined by returns to scale. The long run is a planning and implementation stage.〔 Melvin & Boyes, 2002. ''Microeconomics'', 5th ed., p. 185. Houghton Mifflin.〕〔Boyes, W., 2004. ''The New Managerial Economics'', p. 107. Houghton Mifflin.〕 Here a firm may decide that it needs to produce on a larger scale by building a new plant or adding a production line. The firm may decide that new technology should be incorporated into its production process. The firm thus considers all its long-run production options and selects the optimal combination of inputs and technology for its long-run purposes.〔Melvin & Boyes, 2002. ''Microeconomics'', 5th ed., p. 185. Houghton Mifflin.〕 The optimal combination of inputs is the least-cost combination of inputs for desired level of output when all inputs are variable.〔 Once the decisions are made and implemented and production begins, the firm is operating in the short run with fixed and variable inputs.〔〔 Perloff, J, 2008. ''Microeconomics Theory & Applications with Calculus'', p. 230. Pearson .〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Long run and short run」の詳細全文を読む スポンサード リンク
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