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When the U.S. air force discovered the flaw of averages

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Re: When the U.S. air force discovered the flaw of averages

#31
post #21

joint distribution of 2 normal distributions isn't necessarily a normal distribution in 2 variables. Independence would be sufficient condition for that, yet obviously there is no independence between various measurements of a human body. https://en.wikipedia.org/wiki/Multivariate_normal_distributi...

What are you talking about?

Re: When the U.S. air force discovered the flaw of averages

#32

The concept of no members of a group fitting into the average range for all observations is reminiscent of the 'curse of dimensionality'. Can anyone with a data science background make the connection here? Secondly, this seems to explain why everyone hates autocorrect.

Data science background here. Connection made. Anything else you want?

Re: When the U.S. air force discovered the flaw of averages

#33
post #21

joint distribution of 2 normal distributions isn't necessarily a normal distribution in 2 variables. Independence would be sufficient condition for that, yet obviously there is no independence between various measurements of a human body. https://en.wikipedia.org/wiki/Multivariate_normal_distributi...

I was thinking it was a Venn diagram, where none of the bubbles had complete intersection with the others.

"This bubble represents all pilots between 5'6" and 5'11" in height. And here's the bubble that represents those with 40" chests. Note how they barely intersect."

Re: When the U.S. air force discovered the flaw of averages

#34

Earlier quoted context omitted.

That's assuming that they're independent, though, which is certainly false. I'm curious by how much.

Why is it certainly false?

The simplest example I can come up with is the weight - the density of humans is probably constant for practical purposes and therefore the weight must be positively correlated with your body dimensions. It is also pretty obvious that humans, or tissue for the matter, does not grow in a strongly directional manner. If you gain weight more or less all dimensions not constraint by your skeleton will increase, i.e. you will probably not end up with a wide but flat or narrow but thick belly.

Re: When the U.S. air force discovered the flaw of averages

#35

Articles like this remind me how rational and practical the military is. I know so many brilliant military minds, yet war itself seems outdated and plagued by so many emotionally irrational decisions. I can't reconcile those two thoughts. How can people inside the military be so incredibly smart, yet still think it makes sense to ... you know, kill people's friends and families and not expect them to become terrorist…

I can't speak for the entire military[1], but I've known a few "brilliant military minds" and they rarely, if ever, talk in terms of killing. The military's goals are usually things like area denial, disrupting lines of communication, limiting access to materiel and supplies, degradation of morale, etc.

These aren't just euphemisms. If you're trying to win a war solely by killing the enemy, you're going to be in for a looooong and bloody war. In fact, there's long been a thinking in the military that "a dead soldier removes one soldier from the field, but a wounded soldier removes two".

What makes the military, and war, seem "outdated" or downright "despicable" comes down to, I think, two things:

1. War is often what happens when two sides have let long lingering issues fester to the point that dialogue is not possible. In other words, the only thing anyone wants less than to throw the first punch is to be unable to throw the second.

2. Yes, military industrial complex. Specifically, the MIC has muddled the "goals" and abstracted them away behind many layers of "weapons systems" and "advanced tactics". That is, if you're a general attempting to disrupt lines of communication, and you have to decide on committing the lives of your soldiers and potentially taking the lives of your enemy, you might consider a battle plan that minimizes loss of life. If you're that same general and Raytheon (or Lockheed or Honeywell or...) offers to sell you the CommsRuptor 7000 that will take out enemy communications at the press of a button (and a signature on a check for $300M), you might not adequately question the impact on lives. War used to be about loss of blood and treasure. Lately it seems to be more about treasure and blood...

[1] Especially not the "grunts" that see front-line action. I've heard, anecdotally, that enlisted soldiers are often trained in such a way that they enter war zones with raw blood-lust. Whatever your opinion on this practice, I took from your question that you were more interested in the thinking of the decision-makers, i.e. commissioned officers.

Re: When the U.S. air force discovered the flaw of averages

#36

Articles like this remind me how rational and practical the military is. I know so many brilliant military minds, yet war itself seems outdated and plagued by so many emotionally irrational decisions. I can't reconcile those two thoughts. How can people inside the military be so incredibly smart, yet still think it makes sense to ... you know, kill people's friends and families and not expect them to become terrorist…

The idea that killing a person's friends of family turns them into a terrorist, and that this is the ultimate source of terrorism and terrorists, is an oft-repeated but highly unsupported claim. It's ultimately a cudgel wielded by advocates of particular political ideologies, not serious students of terrorism and counterterrorism.

Re: When the U.S. air force discovered the flaw of averages

#37
Wow! This has implications for human genetics (a study that originated partly in considering human body size measurements like those described in the article) that I think most popular writers on human genetics have not taken into account. There was an article posted to Hacker News earlier this week that suggested, surely falsely in my opinion, that human genomes can be optimized for intelligence to such a degree that we won't even be able to estimate IQ scores for future individuals with the same kind of tests that we use now. I rather doubt it. Because of pleiotropic effects of genes, almost surely there isn't a gene shuffle that will massively increase human intelligence, but rather just strategies (as likely to be environmental as genetic) to improve average intelligence within the range already found in the worldwide human population.

Similarly, imputation of "race" by genome testing depends crucially on assuming that the average genome is informative, but for any trait of interest, a person who by both genome testing and known historical ancestry is categorized in some "race" category might have any degree of variance from "average" in the trait found in the whole human genome. It will be exciting to follow up on larger and larger data sets on these issues as human genomics projects continue.

Re: When the U.S. air force discovered the flaw of averages

#38
post #27
post #4

Is it just me or does this sound oddly familiar to machine learning recommendation systems? ie: show an item based on the average of all the other items that everyone else has looked at.

Yeah, I was thinking of the same thing. It's not my field professionally though, so I am not sure what the relevant conclusion would be for machine learning though (or if the comparison holds at all).

I don't think that's quite correct.

Recommendation engines normally work by taking the things you favor, then looking at who else favors those things, and deducting that you're all likely to have shared interests.

Re: When the U.S. air force discovered the flaw of averages

#39

The concept of no members of a group fitting into the average range for all observations is reminiscent of the 'curse of dimensionality'. Can anyone with a data science background make the connection here? Secondly, this seems to explain why everyone hates autocorrect.

Yes, this can be made precise: For example, consider a uniform distribution on a d-dimensional cube with side length 1. Only a (1/2)^d fraction of the mass is within 0.25 distance of the average in every coordinate. In high dimensions, almost all the mass is "near the boundary" in at least one coordinate.

Or as one of my professor would say (after showing the calculation for n-dimensional spheres): "and that's why infinite dimensional oranges are all skin!"

Re: When the U.S. air force discovered the flaw of averages

#40

Earlier quoted context omitted.

Do military people disagree with your analysis about killing ?

I was really dismayed when Colin Powell argued for invading Iraq. Yes, there are military people who get it. But just look what's happening. I guess they have to think, what is the alternative? We can't change our role in the Middle East. We can't just stop supporting Israel for example. I suppose yes, they tried Camp David. I guess I just want everyone to cease fire. Maybe the overpowered people resorting to terrori…

High star generalship is more politics than military ability at this point.

http://www.theatlantic.com/magazine/archive/2012/11/general-... for one discussion of this.

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