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I migranti di Fahrenheit migrano ancora… (IV inbloggazione)

L’economia è una fiaba per grandi (e le fiabe sono importanti)

Cos’è l’economia? Purtroppo è necessario rispondere a questa domanda per chi vuole criticare o omaggiare gli economisti.

Al momento la risposta migliore è disponibile nel libro di Ariel Rubinstein: Economic Fables. Naturalmente è un’opinione personale, sia chiaro.

Ariel è un economista (forse il più grande teorico dei giochi vivente) che non non conosce bene l’economia (PIL, titoli, opzioni, indici…), non è nemmeno molto interessato ad essa (come tutti noi salta regolarmente la pagina economica dei giornali) e non dà molto credito ai discorsi improntati al gergo economico:

…. I am not sure that I know what an option is; I am not attempting to predict the rate of inflation tomorrow nor the productivity index in manufacturing the day after tomorrow… I would like to state that economic theory is exploited in discussions about current economic issues, and I don’t like it…, to put it mildly…

Come tutti sanno, gli economisti vivono di modelli. Ecco allora un’analogia illuminante:

… The word model sounds more scientific than the word fable or tale, but I think we are talking about the same thing….

Cosa fa un buon cantastorie?:

… The author of a tale seeks to impart a lesson about life to his readers…

Il che è un compito assai nobile:

… It is possible to dismiss any tale on the grounds that it is unrealistic, or that it is too simplistic. But this is also its advantage

Il cantastorie ha un vantaggio sullo scienziato: puo’ dare più spazio alla bellezza e alla semplicità, sebbene non arrivi alla libertà dell’artista:

… free from irrelevant details and unnecessary diversions…

A volte si accusano i modelli economici di essere “semplicistici”. Ma questa, lungi dall’essere un’accusa è una definizione della loro essenza, anche le fiabe sono riduzioni semplicistiche della realtà:

… Economic theory spins tales and calls them models. An economic model is also somewhere between fantasy and reality. Models can be denounced for being simplistic and unrealistic, but modeling is essential because it is the only method we have of clarifying concepts, evaluating assumptions, verifying conclusions and acquiring insights that will serve us when we return from the model to real life…

Ma perché tanta matematica? I cantastorie ne hanno davvero bisogno?

… Formal language imposes self-discipline on the storyteller…

E’ una questione di generi: i giallisti devono essere più rigorosi degli autori fantasy, e gli economisti ancora più rigorosi dei giallisti.

Naturalmente il modello deve poter essere descritto (una favola è pur sempre una narrazione):

… A description of an economic model is like the introduction in a tale, presenting the heroes, their interests and the setting in which they operate….

Tutto cio’ non toglie il fatto che la matematica crei anche molti danni comunicativi:

…However, formal language also has its disadvantages. It creates the illusion of being scientific. Those unfamiliar with formal models tend to regard them as representing “absolute truth,” though they are nothing more than tales…

A volte la matematica fa girare al largo dalla disciplina persone con un vero talento da economisti, peccato:

… From my teaching experience I have learned that even the best economics students with the highest affinity for the subject have difficulty with the language of formal models, perhaps due to their persistent confusion between the formal model and its interpretation…

Un guaio che si riverbera in modo preoccupante nella vita pubblica:

… when it comes to questions of economic policy, the model’s formal mantle enables economists to create the false impression that their pronouncements are scientific and authoritative…

La matematica è anche un modo astuto per neutralizzare le critiche, anche le più evidenti. E’ una funzione tipica del gergo:

… The barrier between the secret formal language and ordinary human speech almost completely prevents anyone who is not a member of the economic fraternity from criticizing “professional” economic claims…

Ma veniamo ora a qualche esempio di “favola” raccontata dall’economia. Si potrebbe partire dalla fiaba dei giornalai di Hotelling:

Two newsvendors compete for the custom of their city’s newspaper readers located along the city’s main street… In a simple version of the model, the freedom of action of each vendor is limited to choosing the location of his stand… At lunchtime, each newspaper reader takes a break from his other pursuits and realizes that he cannot get through the day without reading the newspaper. The reader sees where the two newsvendors are located, and sets out to buy a newspaper from the closest one…. the principles by which the tale’s conclusion is tested – that is, the solution of the two unknowns – can be found in the solution concept. The conventional solution concept for situations like the above is called a Nash equilibrium… the location of each vendor must be the best one for him given the location of the other one… When one vendor is located in the center, the other will have less than half of the market share if he does not set up his stand in the center too…. Nash equilibrium is achieved when both vendors set up their stands in the center… Any other pair of locations is not a Nash equilibrium… We are thus left with a single equilibrium: the two vendors set up in the center. This situation, a single-equilibrium model, is ideal from the perspective of the narrator of the economic tale because the result of the equilibrium can then be regarded as the inevitable conclusion of the tale…

La favola facilita alcune considerazioni:

… the competition leads to an outcome that is not ideal from the buyers’ standpoint. If one of the vendors sets up at a location other than the center, none of the buyers will suffer and some will benefit, i.e., those who are now closer to the nearest one…

Il cantastorie sa raccontare questa favoletta in modi sempre diversi:

… For example, instead of a main street of a city, economists apply the model to a situation in which two cola manufacturers must choose the sugar content in the product… The conclusion drawn from the model in this case is that both manufacturers should produce an identical product…

La versione “politica” della favole è forse ancora più interessante:

… Political scientists interpret each location point on the main street as a political position in a one-dimensional space (political right versus left, for example). Each candidate positions himself on the political map, aspiring to receive the maximum number of votes… if there are two parties operating in the political space, and if the subject of dispute is primarily one-dimensional, the platforms of the two parties will be identical, in the center of the political spectrum…

Naturalmente nella realtà non avremo mai storie del genere: le fiabe non sono la realtà. Tuttavia, chi ha ascoltato con profitto le favole conoscerà meglio le forze basilari che agiscono anche nella realtà: le fiabe le enfatizzano!

Veniamo adesso alla favola dei tre sarti:

… Imagine an island with six hundred residents, all dressed in identical clothes that require mending every month. Three tailors work at mending the clothes. For as long as anyone can remember, the residents of the island have been divided equally between the three tailors… even with great effort, none of them can do more than three hundred repairs a month. The residents feel that there is “hidden unemployment” in the tailoring sector… It seems that two tailors would be enough and that it would be better if one of the tailors were to quit tailoring and find himself another job… One day, the idea of the free market reaches the island. The traditions are shattered and the decrees canceled, and each tailor can decide on the price he charges for repairs… What will happen on the island in the new situation? The continuation of the Tale of the Three Tailors must provide answers to the following questions: Which tailors will remain in this occupation?… we will use a solution concept called competitive equilibrium… this condition demands that precisely two tailors remain in this business… We will now see that there is competitive equilibrium when the price of a repair is $2.50 (or any other price between $2 and $3), and only tailors B and C remain in this business sector… An “invisible hand” generates the competitive equilibrium price and mobilizes the self-interest of the tailors and the islanders to correct the inefficiency created by the traditions and decrees that were recently canceled…

E’ senz’altro la favoletta preferita dagli economisti. Tra i suoi pregi quella di mettere in evidenza alcuni assunti problematici:

Several assumptions in this story are not obvious. First, is it indeed so clear that the tailors will lower their prices after the cancellation of the traditions and decrees? We expect them to act only in pursuit of their own personal interests… Second, let’s assume that the tailors are not so wise and fall into the trap the competitive atmosphere lays for them. Is it clear that the consumers will indeed choose the least expensive tailor?…

La favola è gravida di conseguenze:

… However, the improvement also led to a change in the distribution of income. The situation is worse for the tailors and better for their customers… Is the income distribution better now? Are the tailors now receiving fairer compensation for their work? Is the price for mending clothes now more reasonable? There are no objective answers to these questions…

C’è anche la favola della torta, una delle mie preferite:

A pie is to be divided between two diners; let’s call them A and B. Both want as much of the pie as possible. Without an agreement on how to divide the pie, both will remain without anything… Each day, one side offers a proposal and the second responds, accepting it or rejecting it. Every time one side rejects the proposal submitted to him, he must submit a counter-offer, but not before the next day… From the perspective of each of the two parties involved, each day that passes without an agreement is like losing a part of the pie… Let us stipulate that from A’s perspective, the loss incurred from each day of bargaining is equal to 2% of the pie. B is more impatient and from his perspective the loss from each day of bargaining is equal to 3%.. Here we will use the solution concept called perfect equilibrium… The model perhaps clarifies the common intuition that a player whose time is more expensive is in a weaker negotiating position vis-à-vis a player whose time is less expensive

Molti che hanno visitato certi mercati levantini saranno rinviati da questa favoletta a situazioni molto concrete:

… I was inspired by the market in the Old City in Jerusalem where I occasionally bargained when purchasing a Bedouin rug or Armenian plate. I really hate to bargain. Once, when I was fed up with the bargaining games in the market, I said to a trader, “Why don’t we play a different game: you make an offer and I’ll simply say ‘yes’ or ‘no’ ?… “Tell me, did you think that I thought there was some offer I would make and that you would accept?” And then he added: “For generations, we have bargained in our way and you come and try to change it?”!…

Dopo questi tre esempi, veniamo al dunque: qual è la relazione tra modelli e realtà? Prima possibile risposta (il modello serve a fare previsioni):

… According to one view, an economic model is supposed to serve as a basis for making predictions… According to this approach, a model is supposed to be an objective description of the real world, not a tale… If the model does not provide enough good predictions, it must be augmented with additional details.

Purtroppo arricchire il modello per renderlo predittivo serve solo a distruggerlo:

… But the increased complexity of the model exacts a steep price: it is hard to understand and is difficult to solve

Altra posizione (il modello è un esercizio intellettuale che mi rende più esperto nella materia):

… According to another view, the objective of the economic model is to sharpen perception. A model is an intellectual exercise… Just as a soldier use simulations in training, the economist exercises his intuitions on a model before offering advice. The use of formal models helps to develop our intuitions about the way things occur in life… These economists did not rely on a particular model, but claimed that their work with formal economic models sharpened their senses….

Purtroppo gli economisti, se chiamati ad agire in quanto operatori economici, non si dimostrano delle grandi volpi:

… But I am quite sure that if instead of devoting my adult life to economic models I had engaged in a non-academic profession, I would view life from standpoints that are less abstract but no less useful…

Ma allora perché mai milioni di studenti sono chiamati a studiare questi modelli, magari nella loro versione più ostica, quella matematica. In fondo se proprio uno vuole ascoltare una fiaba ce ne sono di più piacevoli.

E’ chiaro che gli economisti più sensibili nutrono un certo senso di colpa per la loro esistenza:

… We economists are delighted when we find evidence of purposefulness in our work, because we are full of guilty feelings about devoting our lives to meaningless studies when the world faces innumerable problems…

Una soluzione per dare senso all’economia potrebbe essere questa: l’economia espone la logica della vita. Conoscerla è un bene in sè.

… According to this approach, an economic model is not essentially different from a model in logic. A model in logic is not a prediction of how humans judge whether a phrase in ordinary language is true or false. It is not a recommendation for a thinking person and it is not designed to educate people to think correctly. I contend that economics studies the logic of life, but does not engage in predictions or recommendations… We are satisfied even if the economic model is merely interesting

Ecco come conclude l’economista Ariel:

… I do not think that the bargaining models that I myself have studied have significant predictive value; I am not more qualified than any reader (but also not less qualified than my colleagues) to give advice on how to conduct negotiations, and I do not feel that dealing with these models has sharpened my ability to understand the process of bargaining in the market… At most, we find links between natural ways of thinking and bargaining processes. That is all. Yes, I admit that it is tempting for me to think of myself as a teller of tales, a philosopher, a researcher of the social sciences, in fact, anything but an economist… I have limited knowledge of current economic issues. During most of my life, these issues have not interested me. I usually toss the economics section of the newspaper in the bin together with the sections on sports, fashion and health… On the other hand, I am obsessively occupied with denying any interpretation contending that economic models produce conclusions of real value. I feel attracted to economics as a branch of philosophy… If the models we develop in yellow notepads or on blackboards constitute a basis for predicting human behavior, it would be miraculous in my eyes… There are no miracles in economics, but there are wonders. In my studies in the Department of Mathematics in Jerusalem, I learned to see wonders in the world of formalities…

Possiamo concludere che secondo Ariel l’economista è essenzialmente un filosofo che spiega la logica della vita e nulla più.

COMMENTO PERSONALE

Ariel Rubinstein è convincente nel suo resoconto, anche se difficilmente il mainstream si adeguerà mai ad una simile riduzione del suo ruolo: l’economista-scienziato ambisce ai posti di potere e li ottiene. L’istituzione delle banche centrali e la necessità di un loro governo e di una politica monetaria affidabile ha segnato un successo dell’ “economia come scienza” che appare irreversibile.

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