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Nassim Taleb: We should retire the notion of standard deviation

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Re: Nassim Taleb: We should retire the notion of standard deviation

#31

The central limit theorem shows us that unimodal data with lots of independent sources of error tends towards a normal distribution. That description is a good first-pass, descriptive model for lots and lots of contexts, and standard deviation speaks well to normally distributed data. Squaring error isn't just a convenient way to remove sign, it's driven by a lot of data-sets' conformance to the central limit theorem…

Thank you. I don't think it is intellectually honest for Taleb to omit this fact.

Re: Nassim Taleb: We should retire the notion of standard deviation

#35
post #10

Earlier quoted context omitted.

Like this? "But it is not just journalists who fall for the mistake: I recall seeing official documents from the department of commerce and the Federal Reserve partaking of the conflation, even regulators in statements on market volatility. What is worse, Goldstein and I found that a high number of data scientists (many with PhDs) also get confused in real life." It doesn't tell us what happened, it just asserts that…

> which Goldstein? From ClementM above, http://papers.ssrn.com/sol3/papers.cfm?abstract_id=970480

Thank you.

From that paper:

"We first posed this question to 97 portfolio managers, assistant portfolio managers, and analysts employed by investment management companies who were taking part in a professional seminar. The second group of participants comprised 13 Ivy League graduate students preparing for a career in financial engineering. The third group consisted of 16 investment professionals working for a major bank."

From the article:

"What is worse, Goldstein and I found that a high number of data scientists (many with PhDs) also get confused in real life."

I get that "data scientist" is a really broad term at this point, but I don't think it's a very good description of the people quizzed in this paper, if this is the paper he was indeed referring to.

Re: Nassim Taleb: We should retire the notion of standard deviation

#36
I really tried to get through "The Black Swan" and Taleb's writing struck me as so pretentious and self-involved that it made it impossible for me to finish.

He strikes me as someone who is so desperate to be important and recognized that an assertion like this doesn't really surprise me.

Re: Nassim Taleb: We should retire the notion of standard deviation

#38
I sometimes think that progress in the 21st century will be summed up as: "The realization that the normal distribution is not the only way to model data".

Taleb's favorite topic is the "black swan event" which is something that the normal distribution, and the idea of standard deviation, don't model that well. In a normal distribution very extreme events should only happen once in the lifetime of several universes. Of course assuming variation inline with a Gaussian process is at the heart of how the Black-Sholes model calculates risk/volatility/etc.

Benoit Mandelbrot argued that financial markets follow a distribution much more similar to the Cauchy distribution (specifically the Levy distribution) rather than a Gaussian. The problem of course is that the Cauchy distribution is pathological in that it doesn't have a mean or variance, you can calculate similar properties for it (location and scale), but it doesn't obey the central limit theorem so in practice it can be very strange to work with.

The normal distribution is fantastic in that it does appear frequently in nature, is very well behaved, and has been extensively studied. However a great amount of future progress is going to come from wrestling with more challenging distributions, and paying more attention to when assumptions of normality need to be questioned. Of course one of the challenges of this is that the normal distribution is baked into a very large number of our existing statistical tools.

Re: Nassim Taleb: We should retire the notion of standard deviation

#39

So first about the article: >>The notion of standard deviation has confused hordes of scientists What an assertion! It also proved to be very useful for hordes of scientists... what about some examples of confused scientists ? >>There is no scientific reason to use it in statistical investigations in the age of the computer As someone who uses it daily I am eagerly awaiting his argument. >>Say someone just asked you…

Yeah. Eliminating stdev so social scientists don't get confused is the tail wagging the dog.

maybe in an intellectual sense, but a lot more people read http://www.huffingtonpost.com/science/ than http://arxiv.org/

Re: Nassim Taleb: We should retire the notion of standard deviation

#40

So first about the article: >>The notion of standard deviation has confused hordes of scientists What an assertion! It also proved to be very useful for hordes of scientists... what about some examples of confused scientists ? >>There is no scientific reason to use it in statistical investigations in the age of the computer As someone who uses it daily I am eagerly awaiting his argument. >>Say someone just asked you…

The funny thing is I've never used absolute deviation before, so I'm slightly confused by absolute deviation right now as I wrap my head around what it means relative to sigma (which I have used, lightly, for years) and why anyone would want to use it instead...

edit: apparently MAD can refer to either "mean absolute deviation" or "median absolute deviation". Yup, this sure isn't going to confuse anybody.

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