When the U.S. air force discovered the flaw of averages • Hacker News Board

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

#71

Post by Dylan16807 » Sat, Mar 05, 2016, 11:29 PM UTC

keenerd wrote: post #64

sparky_z wrote: post #62

Earlier quoted context omitted.

Assuming a normal distribution instead of a uniform one isn't that outlandishly unreasonable.

He didn't assume a normal distribution. It wasn't "within ±15% of the mean". It was "the middle 30% of the range". This means excluding 70% of the population for each factor, regardless of the distribution. Finding a "normal person" was impossible from the beginning with that approach.

"the middle 30% of the range" is ambiguous. I interpreted it as mean ± .15 * [max - min]

Also it's only impossible from the beginning if you assume the values are uncorrelated. That's an even worse thing to assume than the existence of an 'average person'.

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

#72

Post by Dylan16807 » Sat, Mar 05, 2016, 11:37 PM UTC

sandworm101 wrote: post #65

I don't see the problem. The fact that no person fit the model perfectly doesn't mean that the model was a poor choice. The question shouldn't be whether any customers fit the cockpit perfectly, but how many customers do and do not fit absolutely. You build the legroom so that most legs will fit, and headroom so that most heads will fit. Then as many people as possible shall fit. Everyone will have some dimension tha…

>I don't see the problem. The fact that no person fit the model perfectly doesn't mean that the model was a poor choice.

Did you skip the part about people dying?

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

#73

Post by throwaway_exer » Sun, Mar 06, 2016, 12:48 AM UTC

sandworm101 wrote: post #65

I don't see the problem. The fact that no person fit the model perfectly doesn't mean that the model was a poor choice. The question shouldn't be whether any customers fit the cockpit perfectly, but how many customers do and do not fit absolutely. You build the legroom so that most legs will fit, and headroom so that most heads will fit. Then as many people as possible shall fit. Everyone will have some dimension tha…

> A cockpit is not a suit.

The opposite is true. To fly an airplane with precision, you need to "strap the airplane on."

That means sitting in the position with the best visibility and best reach inside the cockpit, even a Cessna 172.

(In a 172, you should sit high enough to be able to see each of the rivets on top of the cowling.)

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

#74

Post by wpietri » Sun, Mar 06, 2016, 12:52 AM UTC

Retric wrote: post #49

wpietri wrote: post #46

The thing that strikes me here is how much we repeat the mistake of Norma (taking the mythical average body and assuming that differences mean problems) today in talking about people's minds. I started using computers before it was fashionable, before my fellow nerds started being worth billions and ending up on magazine covers. It's hard to describe now how much our difference was seen as wrong, as the sign of a pro…

Modern psychology does not care about average it cares about capable of functioning in society. If you can't avoid say screaming in public that's a problem not just a non issue. Arguably the tolerances might be low, but it's hard to argue with the basic premise. Granted doctors assume if your talking to them you have a problem. But that's arguably a reasonable prior. PS: The extremes of behavior get very far out ther…

I don't know that I agree with your characterization of modern psychology, and I am anyway talking more about psychiatry and its chemical interventions.

But even if I granted your point, you're still demonstrating one aspect of the problem I'm talking about. You suggest that any time there's a mismatch between a person and the society they find themselves in, there's a problem with the person. Rather than with society, or with their expectations or what "functioning" means, or with some other aspect of the situation.

The same thing happened with the pilots. The assumption was that the planes were fine, so any issue must be with the pilots. But the planes were constructed around a mythical "normal" person, and I am suggesting we construct society and our expectations of its participants around a "normal" person.

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

#75

Post by foota » Sun, Mar 06, 2016, 1:14 AM UTC

contravariant wrote: post #58

okintheory wrote: post #9

Earlier quoted context omitted.

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.

Weirdly enough, even the proportion of points within a distance of 1/2 to the midpoint becomes really small for higher dimensions.

takeaway: With enough dimensions everyone is weird

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

#76

Post by sandworm101 » Sun, Mar 06, 2016, 1:15 AM UTC

throwaway_exer wrote: post #73

sandworm101 wrote: post #65

I don't see the problem. The fact that no person fit the model perfectly doesn't mean that the model was a poor choice. The question shouldn't be whether any customers fit the cockpit perfectly, but how many customers do and do not fit absolutely. You build the legroom so that most legs will fit, and headroom so that most heads will fit. Then as many people as possible shall fit. Everyone will have some dimension tha…

> A cockpit is not a suit. The opposite is true. To fly an airplane with precision, you need to "strap the airplane on." That means sitting in the position with the best visibility and best reach inside the cockpit, even a Cessna 172. (In a 172, you should sit high enough to be able to see each of the rivets on top of the cowling.)

Yes, but the seat does adjust. It isn't the case that the cockpit must be tailored to every person. Each Cessna, 747 or f-16 seat is practically interchangeable amongst the type. These aren't WWI biplanes with nothing more than a cushion. Even then, the cushion height, the prime dictator of eye level, is adjustable.

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

#77

Post by beachstartup » Sun, Mar 06, 2016, 1:26 AM UTC

analogous anecdote: if you've ever tried to drive a sports car in a seating/steering/pedal/shifting position that isn't tailored to your body, it feels really awkward and it's very difficult if not impossible to drive fast with precision.

i would guess that in a sports or race car, everything needs to be within a few millimeters of where it "should" be in order for it to feel right. multiply the speeds and divide reaction times by 4-5x and i can see how you could easily crash a plane with a tiny margin for error.

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

#78

Post by [deleted] » Sun, Mar 06, 2016, 1:33 AM UTC

keenerd wrote: post #64

sparky_z wrote: post #62

Earlier quoted context omitted.

Assuming a normal distribution instead of a uniform one isn't that outlandishly unreasonable.

He didn't assume a normal distribution. It wasn't "within ±15% of the mean". It was "the middle 30% of the range". This means excluding 70% of the population for each factor, regardless of the distribution. Finding a "normal person" was impossible from the beginning with that approach.

[deleted]

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

#79

Post by vlehto » Sun, Mar 06, 2016, 1:42 AM UTC

sandworm101 wrote: post #76

throwaway_exer wrote: post #73

Earlier quoted context omitted.

> A cockpit is not a suit. The opposite is true. To fly an airplane with precision, you need to "strap the airplane on." That means sitting in the position with the best visibility and best reach inside the cockpit, even a Cessna 172. (In a 172, you should sit high enough to be able to see each of the rivets on top of the cowling.)

Yes, but the seat does adjust. It isn't the case that the cockpit must be tailored to every person. Each Cessna, 747 or f-16 seat is practically interchangeable amongst the type. These aren't WWI biplanes with nothing more than a cushion. Even then, the cushion height, the prime dictator of eye level, is adjustable.

I don't know about postwar planes, but at least some of the WWII war birds had notoriously poor seat adjustments. For example BF-109 had a seat that doubled as armored fuel tank. It's bit tricky to add adjustments to such heavy piece of furniture, so they didn't.

The thing here, just like you pointed out, is not to tailor the seat for average nor individual, but a range that suits most individuals.

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

#80

Post by muddyrivers » Sun, Mar 06, 2016, 2:05 AM UTC

keenerd wrote: post #59

While hindsight is 20:20, parts of this should have been more obvious. > Daniels generously defined as someone whose measurements were within the middle 30 per cent of the range of values > Daniels discovered that if you picked out just three of the ten dimensions of size ... less than 3.5 per cent of pilots would be average sized on all three dimensions. 30% raised to the third power is 2.7%. Basic probability. I gu…

That is over-simplification. First, the samples are not randomly selected. The selection process tended to lean toward means, based on the article. Second, the variables are not independent. They are strongly correlated. The selection process indicated that the probability of having a pilot with long legs but short arms was close to zero.