Aprendre la diferència entre risc i incertesa, o no

| 04/20/2009 |
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Actualitzar: si vostè està buscant una distinció acadèmica, veure: La diferència entre risc i incertesa. En el post de sota, critiquem les empreses per no canviar les seves pràctiques malgrat els recents fracassos de les seves estimacions, metodologies, i models. Per descomptat, pensem que tots dos són val la pena llegir.

Cada dilluns al matí en els últims anys, hem rebut un correu electrònic a http://jobs.phds.org que les llistes de llocs vacants d'acord amb les nostres especificacions, que són:

“Enviar correus electrònics setmanals que contenen treballs…
…per a doctorats en: Negocis / Finançar / Economia
…de tipus: Contracte / Projecte / Temporary, Employee, Non-tenure-track faculty, Postdoctoral researcher, Tenure-track / tenured faculty
in sectors: tots els
located: in United States
with keywords: none

En general, there’s 20 – 40 positions listed each week, and most of those involve quantitative finance, usually in the NYC area. For the past year or so, we’ve been particularly interested to see if the job descriptions would change given the failure of many quantitative trading strategies, modeling techniques and risk measures. (Sí, we know they didn’t actuallyfail.Recent results were just plain bad luck that no one could have predicted. The models worked perfectly, except when they didn’t.)

Per desgràcia, our parenthetical sarcasm seems to be the implicit position of many financial firmswithout the sarcasm, és clar. We say because we haven’t observed any change in the posted job descriptions in the jobs.phds.org emails or any of the other ones that we receive from recruiters who regularly send similar descriptions.

Ara, we’ve been meaning to write about this observation for a few months but were finally motivated to do so because of several other items we read this morning, including two opinion columns and one article.

L'article, Computer-Trading Models Meet Match a El Wall Street Journal, describes how several algorithmic-based hedge funds have lost money recently because ofthe recent high volatility.” Així que, we guess their models aren’t flawless.

One of the op-ed pieces is per L. Gordon Crovitz, and it is also in the Journala: In Finance, Too, Learning Entails Risk. Hi, El Sr. Crovitz attempts to relatefinancial engineeringto other types of engineering, g, mechanical engineering, and he seems to imply that it’s still a young discipline; el, give it time, but we think that his argument ultimately fails and is unconvincing.

Això és degut a “financial engineeringisn’t really engineering, which we’d define as the thoughtful application of science or technology to (or in) a well-understood, physical environment. Finance is a subset of a socialscience.

El Sr. Crovitz writes in his last paragraph that: “The measure of innovators is not in the mistakes they make, but in the lessons they learn. We now know that our complex markets need better models, which should include more humility, acknowledging that some risks are still too uncertain to measure and should be avoided.We’d argue with thestill tooin the last sentence as we doubt that such social uncertainty can be resolved or precisely measured. (Pel camí, we also disagree with his conclusion in that sentence thatsome risks…should be avoided.We have no problem with folks taking wild or uncertain gambles; però,, we see no reason that we should subsidize their losses when those gambles go bad.)

To his main point, però,, we don’t see much learnin’ Goin’ a. It seems to be business as usual at many firms and funds.

A much more critical op-ed piece is by Michael Barone, and it’s entitled ‘Formulasfor certain failure, and his first sentence isBeware of geeks bearing formulas.He discusses (and criticizes) financial models, global warming/climate change models, and health-care models, and it reads much like our post from six months ago, L'escalfament global i la crisi de les hipoteques. Remember that this is Michael Barone, who is very well-known for using statistical data in the analysis of politics and demographics.

As usual, quin punt els nous lectors del nostre assaig, Gestió de la incertesa, which details our perspective and philosophy on these issues as well as any number of related posts: see our blog archives. The main point is that not all uncertainty is measurable, i, que la incertesa mesurable, o el risc, és un subconjunt propi de la incertesa i el desconeixement. (En altres paraules, les condicions específiques de matemàtiques s'han de complir perquè la incertesa en termes de risc. Així que, la incertesa és un terme més general, i, tots els riscos consisteix en la incertesa, però no tot el que està clar és arriscat perquè no tota la incertesa es pot mesurar, which a specific mathematical definition.)

As we read the evidence, many institutions and their ‘quantswill continue to solve mis-specified risc problemes, because they don’t know how to treat more diffuse and difficult uncertainty problems; el, they assume them away and treat them as risk problems. We’re clearly not underestimating the difficulties these folks face nor the necessity of making trade-offs, but we’re not sure if they understand the nature of the problem or trade-off. As we’ve written many times before, if they don’t understand them, then they are ignorant, and if they do, then they are cynical., g, La nostra pregunta eterna: Cínic o Naive? Neither charactistic is appealing or useful.

Ignoring the larger epistemological issues and the problem of induction, here’s a simple example of the difficulty of making inferences and finding useful information. Even when a distribution can be perfectly known, it’s momentslike the mean and varianceneed not exist. (Look a Cauchy distributions and, més en general, certain stable distributions. While one can calculate historical means and variances from a time series, els “estimacions” may be nonsensical. (They can’t estimate something that doesn’t exist.) The arithmetic can be performed, but the notion is empty.

Tal com ho veiem, too often if one has a (risc) hammer, then everything looks like a (risc) nail, and it’s easy to pound away, especially when the alternate is to admit that a solution doesn’t exist, which too often sounds like, “No ho sé.” Així que, while various numbers can be calculatedeven calculated very precisely, earnestly, and diligentlyto do so is to apply technology, but it’s not engineering nor is it very smart and it can be very harmful.

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