Markov Perfect Industry Dynamics with Many Firms

We propose an approximation method for analyzing Ericson and Pakes (1995)-style dynamic models of imperfect competition. We develop a simple algorithm for computing an ``oblivious equilibrium,'' in which each firm is assumed to make decisions based only on its own state and knowledge of the long run average industry state, but where firms ignore current information about competitors' states. We prove that, as the market becomes large, if the equilibrium distribution of firm states obeys a certain ``light-tail'' condition, then oblivious equilibria closely approximate Markov perfect equilibria. We develop bounds that can be computed to assess the accuracy of the approximation for any given applied problem. Through computational experiments, we find that the method often generates useful approximations for industries with hundreds of firms and in some cases even tens of firms.

Inside the Economist's Mind: The History of Modern Economic Thought, as Explained by Those Who Produced It

This is the front matter from a book of interviews to be published by Blackwell. The book is coedited by W. A. Barnett and P. A. Samuelson. The front matter includes the Table of Contents, Coeditor Preface by W. A. Barnett, Coeditor Foreword by Paul A. Samuelson, and History of Thought Introduction by E. Roy Weintraub. The front matter highlights some of the more startling and controversial statements contained in the interviews and puts the interviews into context relative to the history of modern economic thought. The interviews reprinted in this book include: (1) Wassily Leontief interviewed by Duncan Foley. (2) David Cass interviewed jointly by Steven Spear and Randall Wright. (3) Robert E. Lucas interviewed by Bennett T. McCallum. (4) Janos Kornai interviewed by Olivier Blanchard. (5) Franco Modigliani interviewed by William Barnett and Robert Solow. (6) Milton Friedman interviewed by John Taylor. (7) Paul A. Samuelson interviewed by William A. Barnett. (8) Paul Volcker interviewed by Perry Mehrling. (9) Martin Feldstein interviewed by James Poterba. (10) Christopher Sims interviewed by Lars Peter Hansen. (11) Robert Shiller interviewed by John Campbell. (12) Stanley Fischer interviewed by Olivier Blanchard. (13) Jacques Drèze interviewed by Pierre Dehez and Omar Licandro. (14) Tom Sargent interviewed by George Evans and Seppo Honkapohja. (15) Robert Aumann interviewed by Sergiu Hart. (16) James Tobin and Robert Shiller interviewed by David Colander.history of economic thought, Samuelson, macroeconomics, microeconomics, policy, interviews

Közgazdasági tudományháborúk

Nem újdonság, hogy a közgazdaságtan elmélettörténetét a legtöbb közgazdász lenézi. Szinte évente rendeznek szakmai vitákat az eszmetörténet intézményi szerepéről; mi több, egy 2001-es konferencián a terület ingatag állapotát dokumentálták Észak-Amerikában és még veszélyeztetettebb helyzetét az Egyesült Királyságban és Ausztráliában (Weintraub 2002b). A Duke Egyetem kivételével Észak-Amerika egyetlen „elit” egyetemén sincs köz- gazdaságtan-elmélettörténetből nemhogy rendszeres kurzus, de még program sem (Gayer 2002)

Industry Dynamics: Foundations For Models with an Infinite Number of Firms

This paper explores the connection between three important threads of economic research offering different approaches to studying the dynamics of an industry with heterogeneous firms. Finite models of the form pioneered by Ericson and Pakes (1995) capture the dynamics of a finite number of heterogeneous firms as they compete in an industry, and are typically analyzed using the concept of Markov perfect equilibrium (MPE). Infinite models of the form pioneered by Hopenhayn (1992), on the other hand, consider an infinite number of infinitesimal firms, and are typically analyzed using the concept of stationary equilibrium (SE). A third approach uses oblivious equilibrium (OE), which maintains the simplifying benefits of an infinite model but within the more realistic setting of a finite model. The paper relates these three approaches. The main result of the paper provides conditions under which SE of infinite models approximate MPE of finite models arbitrarily well in asymptotically large markets. Our conditions require that the distribution of firm states in SE obeys a certain “light-tail” condition. In a second set of results, we show that the set of OE of a finite model approaches the set of SE of the infinite model in large markets under a similar light-tail condition.

Investigating domain-specific cognitive impairment among patients with multiple sclerosis using touchscreen cognitive testing in routine clinical care

Cognitive dysfunction is present in up to 70% of patients with multiple sclerosis (MS) and has been reported at all stages and in all subtypes of the disease. These deficits have been reported across a variety of cognitive domains, but are generally under-recognized and incompletely evaluated in routine clinical practice. The aim of this study was to investigate the spectrum of cognitive impairment in patients with MS presenting to a specialist MS clinic using the Cambridge Neuropsychological Test Automated Battery (CANTAB), administered on a touchscreen platform. Ninety MS patients completed computerized CANTAB tasks assessing working memory, executive function, processing speed, attention, and episodic memory. Scores were adjusted for age, sex, and level of education and classified as normal or impaired based on comparison with a large normative data pool. We also investigated the impact of clinical and demographic variables which could potentially influence cognitive performance including patient educational level (a proxy for cognitive reserve), disease status (duration, course, and severity of MS), and depression. CANTAB testing detected cognitive impairment in 40 patients (44% of the sample). The most frequently impaired domain was executive function, present in 55% of cognitively impaired individuals. Disease duration and severity were significantly associated with performance across various cognitive domains. Patients with depressive symptoms were also more likely to exhibit impaired processing speed. Results from this study confirm that cognitive impairment is common and occurs across a range of domains among MS patients attending routine clinical visits. CANTAB tasks provide a sensitive and practical approach to cognitive testing in MS patients as part of a holistic patient assessment

Application of Decision Theory methods for a Community of Madrid Soil classification case

A land classification method was designed for the Community of Madrid (CM), which has lands suitable for either agriculture use or natural spaces. The process started from an extensive previous CM study that contains sets of land attributes with data for 122 types and a minimum-requirements method providing a land quality classification (SQ) for each land. Borrowing some tools from Operations Research (OR) and from Decision Science, that SQ has been complemented by an additive valuation method that involves a more restricted set of 13 representative attributes analysed using Attribute Valuation Functions to obtain a quality index, QI, and by an original composite method that uses a fuzzy set procedure to obtain a combined quality index, CQI, that contains relevant information from both the SQ and the QI methods