John Fraser Muth

John Fraser Muth (27 settembre 1930 – Key West, 23 ottobre 2005) è stato un economista statunitense, noto come padre della rivoluzione economica delle aspettative razionali, in virtù del suo articolo "Rational Expectations and the Theory of Price Movements" del 1961.

Muth, Ph.D. in economia matematica alla Carnegie Mellon University, per primo nel 1954 ha ricevuto il premio Alexander Henderson. Ha svolto attività di ricerca alla Carnegie Mellon dal 1956 al 1959, per poi svolgere l'attività di professore fino al 1964.

Muth sosteneva che le aspettative "sono essenzialmente la stessa cosa delle previsioni della teoria economica. Benché ha formulato il principio delle aspettative razionali in un contesto microeconomico, è stato usato in campo macroeconomico da Robert Lucas, Jr., Finn E. Kydland, Edward C. Prescott, Neil Wallace, Thomas J. Sargent, e altri.

Holt, Modigliani, Muth, and Simon (1960)

Mentre John Muth sviluppava il concetto di aspettative razionali, Herbert A. Simon stava raffinando le sue idee di razionalità limitata, mettendo in luce le limitate capacità di calcolo della gente.

Insieme a due colleghi della GSIA, Charles C. Holt and Franco Modigliani, Muth e Simon hanno scritto un libro sulla programmazione d'impresa. L'obiettivo era di ottenere regole operative facili da applicare. Erano economisti che staano sviluppando modelli differenti, ma cercavano una soluzione allo stesso problema.

Muth (1960)

Phillip Cagan, Milton Friedman e altri hanno usato una versione aggiornata della teoria, la teoria delle aspettative adattive per prevedere la variabile "reddito permanente". In his 1960 paper Muth answered the question for what stochastic process for y will adaptive expectations as postulated by Cagan and Friedman be the optimal forecast of y*. Muth's approach to find recursive optimal linear forecast of a “hidden” state vector, x, given an “observer”, y is very similar to the Kalman filter, presented by Rudolf Kalman in his paper from the same year.

Nel suo scritto "Optimal Properties of Exponentially Weighted Forecasts", pubblicato nel 1960 sul Journal of the American Statistical Association, Muth ha razionalizzatoil modello delle aspettative adattive di Friedman per calcolare il reddito permanente.

Muth (1961)

In contrasto con le teorie di Simon, Muth spinge avanti la sua ipotesi: "Vorrei suggerire che le aspettative, poiché sono previsioni di eventi futuri, sono essenzialmente la stessa cosa delle previsioni della teoria economica" definendo razionali tali aspettative per distinguerle dalle attese di ciò che le imprese dovrebbero fare.

t.b.a.

	« Muth's notion was that the professors [of economics], even if correct in their model of man, could do no better in predicting than could the hog farmer or steelmaker or insurance company. The notion is one of intellectual modesty. [] The common sense is "rationality": therefore Muth called the argument "rational expectations". »
	( Deirdre N. McCloskey, The Rhetoric of Economics, 2, Univ of Wisconsin Press, 1998. ISBN 9780299158149 Page 53. )

Legacy

È difficile trovare settori dell'economia che non sono stati influenzati dai lavori di Muth. Quasi paradossalmente l'alternativa all'ipotesi di Muth deriva dal lavoro del suo collega Simon e dal suo concetto di razionalità limitata.

« Of course we knew about [rational expectations]. Muth was a colleague of ours [in the early 1960s]. We just didn't think it was important. The hypothesis was more or less buried during the '60s. Arrow used it in his paper on learning-by-doing in the '60s. Prescott and I used it in that paper of ours on investment. People were aware of it, but I didn't understand then how fundamental a difference it made econometrically. I didn't realize that if you took it seriously you had to rethink the whole question of testing and estimation. I guess no one else did either, except for Muth. »

(From the interview with Robert E. Lucas by Arjo Klamer, published in Conversations with economists, 1983, ISBN 0-86598-146-9.)

	« It must be quite an experience to write papers that radical and have people just pat you on the head and say 'That's interesting,' and nothing happens. »
	(From the interview with Robert E. Lucas by Arjo Klamer, published in Conversations with economists, 1983, ISBN 0-86598-146-9.)

« Muth's role in the history of economics is unusual. Like Hermann Heinrich Gossen, he became famous for one idea, he provided the analytical key to developments that, in the jargon of scientific journalism, were described as revolutionary, and he was virtually ignored by his immediate contemporaries. However, whereas Gossen had no influence on those developments, his key results being independently rediscovered by Jevons and Walras, the rational expectations economics of the 1970s and 1980s was a direct outgrowth of Muth's seminal idea. In fact, Muth's contribution is one of the relatively few instances in which there is no indication that the history of economics would have taken about the same course in its absence. It was a novel and ingenious idea, it was not "in the air," and no multiple discovery has yet come to light. »

( Jürg Niehans, A History of Economic Theory, The Johns Hopkins University Press, 1990. ISBN 0801838347 Page 509. )

Major works

• Charles C. Holt, Franco Modigliani, John F. Muth, and Herbert A. Simon (1960). Planning Production, Inventories, and Work Force.
• John F. Muth. (1960). "Optimal Properties of Exponentially Weighted Forecasts", JASA
• John F. Muth. (1961). "Rational Expectations and the Theory of Price Movements", Econometrica 29, pp. 315-335.