
Put armor where there aren't bullet holes - robg
http://motherjones.com/kevin-drum/2010/09/counterintuitive-world
======
teilo
This reminds me of the story of the US army moving from canvas to metal
helmets. To their surprise, they found that the number of head injuries went
up, and not down.

Why? Because the metal helmets converted fatalities to head injuries.

~~~
werftgh
Same thing with bicycle helmets and seatbelts in cars.

~~~
ced
This might be closer to the mark:

 _Under the risk compensation theory, helmeted cyclists may be expected to
ride less carefully; this is supported by evidence for other road safety
interventions such as seat belts and anti-lock braking systems. Anecdotally,
many riders report feeling safer with a helmet: "When I wear it, I feel
safe..." One researcher randomized his helmet use over a year of commuting to
work and found that he rode slightly faster with a helmet._

 _Motorists may also alter their behavior toward helmeted cyclists. One small
study from England found that vehicles passed a helmeted cyclist with
measurably less clearance (8.5 cm) than that given to the same cyclist
unhelmeted (out of an average total passing distance of 1.2 to 1.3 metres)._

[http://en.wikipedia.org/wiki/Bicycle_helmet#Risk_compensatio...](http://en.wikipedia.org/wiki/Bicycle_helmet#Risk_compensation)

~~~
brudgers
According to John Forester, being struck by an overtaking car is among the
least likely bicycle accidents, even though it is the rationale used to
justify mandatory bike lane usage. <http://www.johnforester.com/>

His book, _Effective Cycling_ is a great way to improve bicycle safety.

~~~
Vivtek
Reminds me of Neal Stephenson's character whose strategy for bike safety at
night was to assume he was wearing reflective clothing and that everybody in a
car would be paid a million dollars to kill him.

~~~
blasdel
Another strategy is to actually wear OSHA-certified hyper-reflective clothing,
such that the anyone would assume that a driver who hit him must have been
paid a million dollars to do it.

A friend of mine does this, he has a whole closet full of orange and silver
sweatshirts that he wears _every day_. Last time he got hit by a car was years
ago, but when the cops showed up they took one look at him and arrested the
driver before he'd uttered a word.

~~~
jasonkester
Would only work in the US.

Here in England, _everybody_ wears that terrible neon reflective stuff every
time they leave the house. Bicycle optional in many cases. They have no shame
here.

The downside is that it makes me comparatively less easy to spot.

------
BRadmin
Survivorship bias:

<http://en.wikipedia.org/wiki/Survivorship_bias>

~~~
silentbicycle
Would you mind fleshing that out? Just posting two words and linking to
wikipedia doesn't add much to the conversation, and people who care about
maintaining the level of discourse on HN might heavily downvote you.

~~~
bhickey
Suppose that we want to study the underlying genetics of a disease. To do
this, we want to look at some people with the disease (cases) and some people
without (controls). The trouble is that if the disease makes people more
likely to die, they won't be enrolled in your study.

This is of particular concern for fast moving diseases like pancreatic cancer.
In general this effect manifests as a bias against people with more severe
disease -- occasionally these are exactly the people you want to study.

The simplest way to get around this is with an alternative study design.
Rather than ascertaining _cases_ and _controls_ , you enroll a large number of
individuals in a _cohort_. After that, you sit back and track the cohort for
decades and watch for disease to emerge.

A famous example of this is the Religious Orders Study
(<http://www.rush.edu/rumc/page-1099611542043.html>). A large number of
Catholic brothers and sisters graciously agreed to participate on a study of
Alzheimer's disease. The researchers recruited a cohort of non-demented clergy
and have been tracking them for years. They perform annual cognitive tests on
the participants to assess mental decline. All participants were gracious
enough to consent to post-mortem brain donation. It would be impossible to get
this sort of data with a case/control study.

Another type of ascertainment bias is population stratification which can
generate all sorts of misleading results. Imagine that you're a scientist in
Boston and you want to study sickle cell anemia. You phone up a doctor friend
and say "Please send me the next 10 sickle cell cases and the next 10 non-
sickle cell cases." After spending $300,000 and a year and a half on the
project you find some great mutations. Ten minutes later you notice that all
the markers you found are strongly associated with being African-American.
Your cases included 9 persons of African ancestry and one of Mediterranean
ancestry, while your controls matched the particular demographic blend that
you'd expect to find around Boston. Oops.

I hope that helps.

p.s. Is anyone in London looking for smart people? E-mail me. ;)

~~~
werftgh
Similar to the famous Boston cemetery study. It shows the age at death of
people in a cemetery drops linear as you approach the current date. whereas
people 100years ago all died in their 60-80s

------
evgen
For more similar stories check out the
<http://en.wikipedia.org/wiki/Operations_research> wikipedia page.

When google released some OR software recently that hit the HN front page
[<http://news.ycombinator.com/item?id=1724580>] I followed various links to
this particular wikipedia page and then moved on to other things. When the
"armor where there are no bullet holes" stories started popping up I assumed
that this was the event that triggered the "hey this is cool" reaction from a
few people who started the ball rolling...

------
mattmaroon
You must be careful when applying this sort of logic because it assumes that
what happens to a plane after its shot is entirely deterministic, ie. if it
gets shot in the tail fin it crashes, if it gets shot in the wing it doesn't.
That may or may be accurate for planes (I really don't know) but may not for
other things.

Suppose anywhere the plane was shot led to a 1/5 chance of the plane crashing,
meaning that all places are equally deserving of armor. Suppose also that the
wings comprised about 75% of the surface area of the plane. You'd see 3 planes
returning with bullet holes in a wing for every 1 with a bullet hole somewhere
else. That doesn't mean somewhere else is a better place to put the armor.

It's easy to see how it could be possible, if the odds of a crash weren't
uniform (ie if the wings had a slightly higher than average chance of causing
a crash if shot in my example above) you could easily come to the wrong
conclusion.

~~~
kd0amg
_Suppose anywhere the plane was shot led to a 1/5 chance of the plane
crashing, meaning that all places are equally deserving of armor. Suppose also
that the wings comprised about 75% of the surface area of the plane. You'd see
3 planes returning with bullet holes in a wing for every 1 with a bullet hole
somewhere else._

So do your study with the plane divided up into equal-sized sections. Or look
for clustering and divide it based on that.

~~~
jessriedel
Yea. The key assumption for the "put the armor where the bullets aren't" is
that the initial bullets are spread evenly over the surface area (or, rather,
that the bullets are spread evenly over the cross-section, which you then
average over the typical orientation of the plane as it takes enemy fire).
This turns out to be a good assumption because planes typically take highly
dispersed enemy fire compared to the size of the plane.

On the other hand, if the enemy had extremely accurate guns and (say, for
visibility reasons) always shot at and hit particular parts of the plane (say,
the parts of the wings next to the necessarily shiny propellers) then the
naive reasoning would be _correct_ : the areas that were bullet-ridden on
returning planes would be the ones that should be armored.

------
vl
Reminds me of common belief that dolphins push drowning people to the shore.
It's hard to check if it's actually true, after all, most people pushed in
opposite direction are most likely dead.

~~~
gaius
There was an article about this in the paper recently, specifically about
dolphins protecting swimmers from sharks. The scientist said, dolphins are
curious about you because you're warm-blooded like they are. They usually have
their kids with them, so they will make sure the area is shark-free for that
reason. If you don't get rescued before the dolphins get bored, they'll leave
you to the sharks without a second's thought...

------
Luc
It's a nice story, but the distribution of the bullet holes in the
illustration (
[http://motherjones.com/files/images/blog_raf_bullet_holes.jp...](http://motherjones.com/files/images/blog_raf_bullet_holes.jpg)
) looks a bit too neat to me. I wouldn't expect the bullet holes to be placed
exactly so that a cursory glance makes it mind-blowingly obvious where the
weak spots are, in a neatly symmetrical way. I'd expect a bit of frowning and
thinking and calculating to be needed to figure that out.

So, for an article about 'obvious but wrong' conclusions, I think the
illustration is kind of deceiving... unless I'm wrong!

~~~
VMG
Maybe this is the sum of multiple planes illustrated on one

~~~
Luc
That's what it's purporting to be, but maybe it's just made up.

Look here: <http://404uxd.com/2007/08/03/thinking-and-leaping>

In reference to the illustration in question, it says "the result was a
graphic that looked something like the image below", in other words it's made
up.

------
njharman
> count up all the bullet holes in various places, and then put extra armor in
> the areas that attracted the most fire. > > Obvious but wrong

Please tell me I'm not the only one who instantly thought, obviously wrong.
And thought the obvious solution is look at what got shot down (or similar
such as the article listed)

Really? Are most people this illogical?

~~~
pg
It's not _completely_ illogical to want to protect the places with holes,
because the distribution of where bullets hit isn't random. Fighter pilots
aimed at specific parts of planes they were attacking. And some surfaces would
have been protected either by other surfaces or by having a nearly flat angle
of incidence to probable incoming fire.

~~~
robg
I thought this too, but then realized the humans doing the shooting are also
illogical. For instance, I could see how hitting the wings might feel
effective and easy, but it's not a great strategy because the bullet holes
don't really impact the flight capability.

~~~
pg
WW II fighter pilots were very rational about what they aimed at. (I happen to
have read a lot about this.)

~~~
petenixey
Was this because of their incredibly short ammunition reserves? I heard
something recently about spitfires having only having about 20s worth of
machine gun fire.

~~~
stan_rogers
Partly, and in the case of Spitfires and Hurricanes (never forget the
Hurricanes -- they weren't nearly as pretty, but they were every bit as
effective) partly because of the limited structural damage that the .303 round
could do. Later variants were more heavily armed, but the Battle of Britain
was fought primarily with Brownings chambered for the .303 British. That
pretty much left pilots, the cylinders of radial engines and pressurized fuel
and oil systems as the vulnerable points. (Those with .50 Brownings and 20mm
auto cannon could afford to shoot at other things, but a fuselage hit still
rarely did more than add ventilation.)

------
TGJ
I guess an interesting point to think about, of those 1000 or so shots on the
wing, what about the one that finally hit the wire that disconnected the
aileron from the yoke? You might have plenty that hit around the wing, but one
that takes out that wire and it could be over. The sweeping logic being used
doesn't cover those areas.

~~~
Someone
You aren't taking the circumstances into account. The question these guys got
wasn't to optimize plane safety, it was more something like "we will be
building 1000 more of these planes next week. What should we different about
them to make them better?" There simply wasn't time for nuance.

------
maeon3
You can't just say (Bullet hole here) + (returned plane) = (don't need to as
much armor there). You also need to understand the circumstances of how the
plane returned. Was it crippled and just barely made it back with critical
systems straining? Or was it mostly functional?

If there was a common place where planes were shot that caused the airplane to
fly home for an emergency landing, then that spot is a good place for armor.

~~~
bricestacey
Not necessarily. I'm assuming adding armor incurs some form of debt so to
speak on performance, cost, development time, etc. In some cases those debts
might overshadow the cost of armor...

~~~
msbarnett
The related factors of weight, speed, and fuel consumption would be the
obvious downsides to adding armor. Especially considering that a heavier,
slower plane is an easier target, thicker skinned or not.

There's a fine balancing point between just enough and too much armor.

------
aneth
Startup lesson: focus on what functions, what your customers use, and your
core competencies, not fixing things no body is using anyway.

An example of a company I think not following this advice: Pivotal Labs. Why
are they not building premium options into Pivotal Tracker instead of building
WebOS apps?

------
jayliew
<http://en.wikipedia.org/wiki/Black_swan_theory>

~~~
firebones
The only black swan connection I see is Taleb's point about "the graveyard of
silent evidence". Absence of evidence is not evidence of absence. We didn't
see all the planes returning that had catastrophic failures in the known
bullet-holed areas and never returned.

~~~
revorad
"Absence of evidence is not evidence of absence"

I think Eliezer Yudkowsky strongly disagrees -
[http://lesswrong.com/lw/ih/absence_of_evidence_is_evidence_o...](http://lesswrong.com/lw/ih/absence_of_evidence_is_evidence_of_absence/)

