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"In fact, whenever people make decisions after being supplied with the standard deviation number, they act as if it were the expected mean deviation."

Boy, is that statement useless without any kind of context, example or citation.



- Strips a statement of context, examples, and citations.

- Claims it is useless therewithout.


No. There are absolutely no citations or specific examples. There is the claim that "every time a newspaper has attempted to clarify the concept of market 'volatility', it defined it verbally as mean deviation yet produced the numerical measure of the (higher) standard deviation," which is not an example, it's a fact claim without a shred of evidence behind it (and as it is an absolute claim, you only need to find one example of a journalistic article on the stock market that properly defines standard deviation to prove it wrong).


The worst part about this is that it makes Taleb appear to be a complete idiot. Volatility under the Black-Scholes is the standard deviation of the daily price changes (log adjusted) not the standard deviation of the daily price. When the daily newspaper has a better understanding than the supposed expert it is just time to stop listening to said expert.


The next two paragraphs have examples with some context.


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 it did in certain contexts. It doesn't cite the paper he presumably wrote with Goldstein (which Goldstein?) about it. I feel like I'm getting a summary of an abstract with all the citations missing.


> 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.


And all his examples come from the financial sector, it would seem, but in the article he refers to "hordes of scientists," "people in social science," and even "problems with social and biological science." So even the hard sciences get pulled into his indictment of standard deviation, even though he never once gives an example from them.


Wherein the author makes the suspect claim that newspapers discussing the stock market always define standard deviation using the definition for mean deviation.




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