terça-feira, 11 de outubro de 2011

Economistas Têm Alguma Utilidade?

Interessante texto de John Kay, no Financial Times, de agosto deste ano, mas só agora li. Não vou reproduzir todo o texto, pois o FT pede que isto não seja feito, uma vez que cobra para acessar os artigos, mas aqui vão algumas partes importantes. Clique no título para acessar texto completo.

Financial Times - August 25, 2011

The reputation of economists, never high, has been a casualty of the global crisis. Ever since the world’s financial system teetered on the abyss following the collapse of Lehman Brothers three years ago next month, critics from Queen Elizabeth II downwards have posed one uncomfortable yet highly pertinent question: are economists of any use at all?

If you ask why economists persist in making predictions despite these difficulties, the answer is that few do. Yet that still leaves a vocal minority who have responded cynically to the insatiable public demand for forecasts. Mostly they are employed in the financial sector – for their entertainment value rather than their advice. Economists often make unrealistic assumptions but so do physicists, and for good reasons. Physicists will describe motion on frictionless plains or gravity in a world without air resistance. Not because anyone believes that the world is frictionless and airless, but because it is too difficult to study everything at once. A simplifying model eliminates confounding factors and focuses on a particular issue of interest. This is as legitimate a method in economics as in physics.

Since there are easy responses to these common criticisms of bad predictions and unrealistic assumptions, attacks on the profession are ignored by professional academic economists, who complain that the critics do not understand what economists really do. But if the critics did understand what economists really do, public criticism might be more severe yet.

The two branches of economics most relevant to the recent crisis are macroeconomics and financial economics. Macroeconomics deals with growth and business cycles. Its dominant paradigm is known as “dynamic stochastic general equilibrium” (thankfully abbreviated to DSGE) – a complex model structure that seeks to incorporate, in a single framework, time, risk and the need to take account of the behaviour of many different companies and households.

A close relationship exists between these three theories. But the account of recent events given by proponents of these models was comprehensively false. They proclaimed stability where there was impending crisis, and market efficiency where there was gross asset mispricing.

In his presidential lecture to the American Economic Association in 2003, Robert Lucas of the University of Chicago, the Nobel prizewinning doyen of modern macroeconomics, claimed that “macroeconomics has succeeded: its central problem of depression prevention has been solved”. Prof Lucas based his assertion on the institutional innovations noted by Mr Greenspan and the IMF authors, and the deeper theoretical insights that he and his colleagues claimed to have derived from models based on DSGE and the capital asset pricing model.


Another line of attack would discard altogether the idea that the economic world can be described by any universal model in which all key relationships are predetermined. Economic behaviour is influenced by technologies and cultures, which evolve in ways that are certainly not random but that cannot be fully, or perhaps at all, described by the kinds of variables and equations with which economists are familiar. The future is radically uncertain and models, when employed, must be context specific.

But you would not nowadays be able to publish similar work in a good economics journal. You would be told that your model was theoretically inadequate – it lacked rigour, failed to demonstrate consistency. To be “ad hoc” is a cardinal sin. Rigour and consistency are the two most powerful words in economics today.

. . .

Consistency and rigour are features of a deductive approach, which draws conclusions from a group of axioms – and whose empirical relevance depends entirely on the universal validity of the axioms. The only descriptions that fully meet the requirements of consistency and rigour are completely artificial worlds, such as the “plug-and-play” environments of DSGE – or the Grand Theft Auto computer game.

For many people, deductive reasoning is the mark of science: induction – in which the argument is derived from the subject matter – is the characteristic method of history or literary criticism. But this is an artificial, exaggerated distinction. Scientific progress – not just in applied subjects such as engineering and medicine but also in more theoretical subjects including physics – is frequently the result of observation that something does work, which runs far ahead of any understanding of why it works.

Not within the economics profession. There, deductive reasoning based on logical inference from a specific set of a priori deductions is “exactly the right way to do things”. What is absurd is not the use of the deductive method but the claim to exclusivity made for it. This debate is not simply about mathematics versus poetry. Deductive reasoning necessarily draws on mathematics and formal logic: inductive reasoning, based on experience and above all careful observation, will often make use of statistics and mathematics.

The writer, an FT columnist, is a visiting professor at the London School of Economics and a fellow of St John’s College, Oxford

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