Em defesa do "agente racional"

Why use rational choice models?, por "Upholding Economics":

A particular focus of criticism of mainstream economics is the use of rational choice in many orthodox models. Some critics are so extreme as to claim the use of rational choice should invalidate a model a priori. In reality there are many sensible reasons rational choice was and is still used commonly in economics:

Many results in behavioural economics come from small scale experiments in the form of simple games or challenges a small group of test subjects, often students, take part in. Some critics have challenged the external validity of these experiments and their application to the situations economists usually study, which might include seasoned entrepreneurs rather than nervous test participants unfamiliar to the ‘game’. Richard McKenzie emphasizes this point on his work defending the use of rationality. For instance, Richard McKenzie challenges the work of Kahneman for assuming that people favouring a ‘sure thing’ (option A: $800) over a gamble (option B: 85% chance of $1000, 15% chance of nothing) contradicts rational choice , he writes:

“What the behavioralists miss is that variance in outcomes is also consequential in assessing options. Option A has no variance; Option B has a substantial variance, with the outcome ranging from zero to $1,000. Hence, for many choosers, Option A can be more valuable than Option B. Indeed, if expected value were all that mattered, people would never buy insurance. Is the purchase of insurance irrational?”

He goes on to demonstrate how framing choice problems like these in a more relevant entrepreneurial/investment setting, with more realistic outcomes and pay-offs, allowing for repeats of the test to account for learning, and ensuring the students of a personal/financial stake in the choice they make causes the behaviour of the students to converge towards rational choice as predicted by conventional theory. (...)

This of course corroborates previous studies that find experience is both a ‘catalyst’ for rationality and a ‘filter’ of irrationality, where aggregated market outcomes “quickly converge to neoclassical predictions.” To summarise, the results showing irrationality from first generation of economic experiments, often involving students in very limited scenarios with no personal stake, are not necessarily applicable to real world markets and scenarios — while there is strong evidence that real world market experience causes individuals to converge towards rational choice. (...)

One alternative to using rational choice is to explicitly model irregularities and biases as if they are a consistent aspect of behaviour which can be used to make predictions. There is a challenge with this approach however: self awareness.

Many studies have shown that anomalies (divergences from what an efficient ‘rational’ market would produce) in asset pricing behaviour soon disappear once papers are published on their existence. This strongly suggests that behavioural irregularities in relevant economic scenarios cannot be relied upon to be persistent, and because of this may not be suitable for use in long term predictive models.

Uma nota especial acerca da preferência por um resultado certo a um jogo com valor esperado superior - se os comportamentalistas usam esse exemplo para dizer que os agentes não são racionais, então isso não tem ponta onde se lhe pegue; esse é exatamente o resultado previsto pelo modelo do agente racional (aversão ao risco). Fariam mais sentido se usassem o exemplo oposto (como, aliás, de certo modo o João Vasco parece-me fazer aqui): de que muitas vezes as pessoas preferem resultados incertos a um valor certo, mesmo quando o resultado esperado é igual ou até inferior (de qualquer maneira, eu suponho que mesmo isso poderá ser enquadrado no modelo do agente racional - quase toda a gente que faz o totoloto sabe que em média perde-se mais do que ganha, logo suspeito que não é bem uma questão de "irracionalidade" mas de preferências mais complexas do que os modelos tradicionais postulam; pode ser que ainda faça um post sobre isso).