Parachute use to prevent death and major trauma due to gravitational challenge

http://www.bmj.com/content/327/7429/1459

by gmac • 14 years ago

110 57 14 years ago

cstross4• 14 years ago

Best understood in context as a combination of medical humour, and a critique of evidence-based medicine. In this case pointing out the lack of controlled randomized trials of parachutes, and how this would affect the evaluation of the efficacy of parachutes as a life-saving medical intervention.

finnw• 14 years ago

This must once have been true of seatbelts too, before all the experiments that were done with dummies and cadavers.

One could argue that similar experiments should be done with parachutes: Throwing dummies and cadavers out of aircraft onto various surfaces (rock, grass, woodland etc.)

Interesting engineering problem too (you need a robot to pull the ripcord, but then it needs to get out of the way so it does not interfere with the outcome by causing additional injuries, adding too much weight etc.)

varjag• 14 years ago

You don't need a robot, systems that pull ripcord out on exit are used since WW2 in the military.

crntaylor• 14 years ago

The piece of technology you're after is a static line: http://en.wikipedia.org/wiki/Static_line

cstross4• 14 years ago

The problem here is that we have a condition ("jumping out of aeroplanes") where, without an intervention ("give the patient a parachute") the consequences are almost certainly fatal (yes, a handful of people have survived falls from altitude without parachutes: but a fatal outcome is sufficiently certain that defenestration has historically been used as a means of execution).

It's a major ethics no-no to expose healthy patients to potentially-fatal environments. It's also a major ethics no-no to withhold known life-saving treatment in the name of continuing a trial. So we can't contrive a proper randomized double-blind placebo-controlled test of the life-saving efficacy of parachutes, where we push people out of planes repeatedly to see how many survive without a parachute vs. with a parachute.

We can't test parachutes any more than we can contrive an evidence-based test of the efficacy of being-rescued-from-burning-buildings-by-firefighters, by arranging for a city's fire department to randomly not rescue half the victims of house fires, so that we can subsequently compare their survival rate with the survival rate of those who were rescued.

Basically, evidence-based assessment of medical treatments breaks down when it hits the edge condition defined by the patients automatically dying if not treated. At best we can compare different types of parachute, or different types of emergency tratment, and see which has a lower associated mortality rate. But we can't, ethically, compare treatment/no-treatment if there's a high likelihood of no-treatment resulting in death.

gwern4• 14 years ago

> This must once have been true of seatbelts too, before all the experiments that were done with dummies and cadavers.

Surprisingly enough, it was true of airbags after those experiments too: in the late '80s and early '90s, it was noticed that the airbag fatality rate was shockingly high compared to what had been projected, so they went back to the drawing boards and revised the designs. A quote from a RAND study on autonomous cars:

> This tension produced "a standoff between airbag proponents and the automakers that resulted in contentious debates, several court cases, and very few airbags" (Wetmore, 2004, p. 391). In 1984, the US DOT passed a ruling requiring vehicles manufactured after 1990 to be equipped with some type of passive restraint system (e.g., air bags or automatic seat belts) (Wetmore, 2004); in 1991, this regulation was amended to require air bags in particular in all automobiles by 1999 (Pub. L. No. 102-240). The mandatory performance standards in the FMVSS further required air bags to protect an unbelted adult male passenger in a head-on, 30 mph crash. Additionally, by 1990, the situation had changed dramatically, and air bags were being installed in millions of cars. Wetmore attributes this development to three factors: First, technology had advanced to enable air-bag deployment with high reliability; second, public attitude shifted, and safety features became important factors for consumers; and, third, air bags were no longer being promoted as replacements but as supplements to seat belts, which resulted in a sharing of responsibility between manufacturers and passengers and lessened manufacturers' potential liability (Wetmore, 2004). While air bags have certainly saved many lives, they have not lived up to original expectations: In 1977, NHTSA estimated that air bags would save on the order of 9,000 lives per year and based its regulations on these expectations (Thompson, Segui-Gomez, and Graham, 2002). Today, by contrast, NHTSA calculates that air bags saved 8,369 lives in the 14 years between 1987 and 2001 (Glassbrenner, undated). Simultaneously, however, it has become evident that air bags pose a risk to many passengers, particularly smaller passengers, such as women of small stature, the elderly, and children. NHTSA (2008a) determined that 291 deaths were caused by air bags between 1990 and July 2008, primarily due to the extreme force that is necessary to meet the performance standard of protecting the unbelted adult male passenger. Houston and Richardson (2000) describe the strong reaction to these losses and a backlash against air bags, despite their benefits. The unintended consequences of air bags have led to technology developments and changes to standards and regulations. Between 1997 and 2000, NHTSA developed a number of interim solutions designed to reduce the risks of air bags, including on-off switches and deployment with less force (Ho, 2006). Simultaneously, safer air bags, called advanced air bags, were developed that deploy with a force tailored to the occupant by taking into account the seat position, belt usage, occupant weight, and other factors. In 2000, NHTSA mandated that the introduction of these advanced air bags begin in 2003 and that, by 2006, every new passenger vehicle would include these safety measures (NHTSA, 2000).

blahedo• 14 years ago

Yes; as seen in the first footnote:

Contributors GCSS had the original idea. JPP tried to talk him out of it. JPP did the first literature search but GCSS lost it. GCSS drafted the manuscript but JPP deleted all the best jokes. GCSS is the guarantor, and JPP says it serves him right.

raverbashing• 14 years ago

Yes.

All evidence of parachute efficacy is anecdotal (as well as the occasions where the parachute failure "allegedly" caused the death of a person.

Enough with this pseudoscientific babble that parachutes work!!

I love this kind of humor, EBM is certainly important, but some people try to make all and everything out of something.

praptak2• 14 years ago

Media report: "SCIENTISTS CONFIRM: PARACHUTES INEFFECTIVE" "JUMPING OFF A PLANE WITHOUT A PARACHUTE CONSIDERED SAFE"

joelthelion• 14 years ago

That's basically how the media report every little doubt in global warming research.

ktizo2• 14 years ago

Or in the UK's sunday sport: "MOON BUS FELL ON SPACE DENTIST"

aaron695• 14 years ago

So what's the catch? Why is it wrong?

Is it we know lesser falls cause death and as such we can extrapolate out.

Or since the differences are so pronounced there is no need for randomised placebo trails?

glenra• 14 years ago

It's not really wrong. It makes the correct point that randomized controlled trials are only one kind of useful knowledge. It's possible to know stuff that can't be tested that way, so blind insistence on EBM is likely to throw out some babies along with all that bathwater.

Seth Roberts often makes similar points in his blog - people running experiments on themselves of size N=1 can often discover stuff that is useful, even vital, but can't be discovered or demonstrated in a big double-blind study.

Imagine that we had no scruples and were willing to throw people out of aircrafts with dummy or with real parachutes. The ones who had parachutes would still notice when the parachute opened and slowed their fall. So we can't rule out the placebo effect! :-)

trhtrsh• 14 years ago

You could link the ripcord to release a toxin to cause unconsciousness.

stereo• 14 years ago

This is actually quite relevant for bicycle helmets. There is no evidence that they actually make you safer, and the debate can get very passionate.

deltaqueue• 14 years ago

Maybe I'm missing the point of this entire thread and don't truly grasp the argument for EBM vs. correlation, but can someone explain why a statistically significant correlation for this kind of efficacy is not evidence in and of itself?

http://www.sciencedirect.com/science/article/pii/S0001457500...

andrewcooke• 14 years ago

i believe (from memory) that the argument is that wearing helmets deters people from cycling which has a cost in terms of deaths from conditions related to lack of exercise.

(and that's a broader argument than the one covered by the paper you link to)

streptomycin• 14 years ago

Those aren't prospective randomized controlled trials. They're retrospective observational studies. They are evidence of efficacy, no doubt, but not particularly convincing evidence for all the normal reasons observational studies are often unconvincing, but maybe even moreso in light of some other contradictory results in the literature as well as the general concept of risk compensation (i.e., it's not like a parachute where it's very clearly obvious that it works).

csmattryder• 14 years ago

I love our sense of humour, very British:

"Contributors GCSS had the original idea. JPP tried to talk him out of it. JPP did the first literature search but GCSS lost it. GCSS drafted the manuscript but JPP deleted all the best jokes. GCSS is the guarantor, and JPP says it serves him right."

paulsutter2• 14 years ago

Where's the post from tokenadult about the methodological shortcomings of this paper?

tisme• 14 years ago

Right here:

http://news.ycombinator.com/item?id=4644687

linker3000• 14 years ago

...for all values of gravity?

bilbo0s• 14 years ago

Hilarious!

Doesn't it get just RIDICULOUS reading some EBM stuff.

wcoenen• 14 years ago

I see the point they're trying to make, but randomized controlled trials would still be valuable to determine the relative effectiveness of different parachute designs.

tokenadult2• 14 years ago

Some of the comments made by HN participants who posted during the first hour this 2003 article was posted bring up the main point: clinical trials should be informed by prior probabilities. That's why some medical researchers, while not saying that clinical trials are a bad idea, identify the best practice as "science-based medicine" (medicine that takes into account prior probabilities and basic principles of science when evaluating clinical trials) rather than "evidence-based medicine" (which many observers take to be a designation for relying on clinical trials to evaluate treatments). The "About" page on the Science-Based Medicine group blog site puts it well:

http://www.sciencebasedmedicine.org/index.php/about-science-...

"Good science is the best and only way to determine which treatments and products are truly safe and effective. That idea is already formalized in a movement known as evidence-based medicine (EBM). EBM is a vital and positive influence on the practice of medicine, but it has limitations and problems in practice: it often overemphasizes the value of evidence from clinical trials alone, with some unintended consequences, such as taxpayer dollars spent on 'more research' of questionable value. The idea of SBM is not to compete with EBM, but a call to enhance it with a broader view: to answer the question 'what works?' we must give more importance to our cumulative scientific knowledge from all relevant disciplines."

The previous comments posted here mentioning what we can know about falling human bodies from first principles of how free fall in the earth's near gravitational field works, or by experiments with dummies including instruments, or by historical experience with aircraft disasters, correctly point out that randomized controlled trials should be designed with all the relevant science in mind. Further, clinical trials should be designed both to gain knowledge of the effectiveness of varying treatments and to minimize risk to human subjects of treatments (jumping out of an airplane without a parachute, for example, or using acupuncture, for another example) with no strong evidence of effectiveness.

See my all-time favorite link to share in HN comments, LISP hacker and rocket scientist (and now director of research at Google) Peter Norvig's article "Warning Signs in Experimental Design and Interpretation"

http://norvig.com/experiment-design.html

on how to interpret scientific research.

AFTER EDIT: In answer to the question, "Where is the evidence that EBM or SBM helps?", the evidence is all around you, all over the world. I've lived in more than one country, and I have had access to the research library of a major university health sciences center since I was in high school, and the incremental improvements in human lifespan at all ages, young and old, and the reduction in disease burden from all kinds of diseases

http://www.scientificamerican.com/article.cfm?id=longevity-w...

are an outcome caused in large part by better understanding of how to prevent or treat disease, an understanding that comes about from science-based medicine.

The article I just submitted today

http://news.ycombinator.com/item?id=4644708

about systematic reviews of acupuncture research in China illustrates the drawbacks of doing anything but science-based research on human disease prevention and treatment. People can imagine that a lot of speculative treatments work, but the way to demonstrate that one treatment or another works is to investigate it carefully with the underlying science in mind.

pella2• 14 years ago

Where is the evidence that EBM or SBM helps?

praptak2• 14 years ago

You mean where's the evidence that evidence based medicine works?

I could produce some evidence but I'm afraid that then you'd ask me where's the evidence that my evidence actually supports the hypothesis that evidence based medicine actually helps.

ktizo2• 14 years ago

Lots of old people. Though that might just be down to the decrease in witch burnings as a method of driving out plague. Hard to tell for sure unless we count them, but there does seem to be loads of them about.

paulsutter2• 14 years ago

Peter Norvig may be an expert on scientific methodology, but when it comes to comedy he's not the first source I would turn to. Steve Martin, an authority in the field, said "Comedy is not pretty"[1] and that clearly overrides Norvig in the matter of this article.

George Carlin makes many excellent points on the subject of science, but most relevant here is when he raises the question of which party is really the subject of an experiment[2].

"The truth is, Pavlov's dog trained Pavlov to ring this bell just before the dog salivated." -George Carlin

Perhaps the real study here is to test how many people will take a joke a little too seriously just because it looks like a scientific paper.

[1] http://en.m.wikipedia.org/wiki/Comedy_Is_Not_Pretty!

[2] http://todayinsci.com/C/Carlin_George/CarlinGeorge-Quotation...

tokenadult2• 14 years ago

Peter Norvig may be an expert on scientific methodology, but when it comes to comedy he's not the first source I would turn to.

Peter Norvig is in the top ten when it comes to humorous commentary on the foibles of PowerPoint.

http://norvig.com/Gettysburg/index.htm

The serious author on that subject is Edward Tufte.

http://www.edwardtufte.com/bboard/q-and-a-fetch-msg?msg_id=0...

Zarkonnen• 14 years ago

This is kind of making me froth: of course parachutes are tested. Lots and lots of R&D time has gone into developing better crew/passenger escape system for aircraft.

The authors are simply whining about evidence-based medicine, which is now finally being pushed after a realisation that a lot of the medical interventions we use are based on gut feeling, hearsay, or ancient, tiny, badly-implemented trials.

Human beings are extremely good at seeing patterns where there are none. We need good, solid stats to keep us grounded in reality.

gwern4• 14 years ago

Yeah, The problem is always that very few, very few indeed, medical procedure rises to the prior that parachutes have... but anti-EBM people somehow have a surprisingly long list of such procedures, a list that rather resembles the list they would've made before EBM began insisting on RCTs.

beagle33• 14 years ago

I like EBM. I would love to live in a world in which it is practiced properly. One of the biggest problems with EBM, though, is that what often is advertised EBM, actually isn't.

My ex was a medical doctor, and for fun I used to read NEMJ and BMJ articles through her subscription. If you trace through references, you often find a (reasonably rigorous) study with reasonable effect observed on a group 40 norwegian women aged 40-50; which in a later article referencing it is assumed to apply to all women in that age group; and through the years is assumed to apply to all women in all age groups. And that's the part that is "easy" to trace (except no one ever does, and it's not really easy)

Additionally, the statistical evidence is inherently weaker than is presented (in a way which no one can actually evaluate) due to the lack of accounting for negative results and unreported trials.

Also, accepted login in EBM is not acceptable from a math perspective. Seth Robert's recent blog post gives a striking example: http://blog.sethroberts.net/2012/10/11/jama-jumps-to-conclus... ; Tell someone about YOUR (n=1, but better controlled than most medical tests!) experiment with Vitamin D, and they'll likely counter with "Oh, but that has been refuted. It's just placebo". That's a big percentage of how EBM is used in practice. And that's the part I don't like.

pella2• 14 years ago

A humorous article in the BMJ that describes evidence-based medicine (EBM) as a religion:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC139053/

ck2• 14 years ago

http://en.wikipedia.org/wiki/Annals_of_Improbable_Research#N...

clueless1233• 14 years ago

Sign at the loading ramp at Zephyrhills Skydiving center: "Gravity is the law, obey the law!"

wac• 14 years ago

Can I just point out that the BMJ's Christmas issue always includes 'humourous' pieces of research:

In 2011:

"Is 27 really a dangerous age for famous musicians? Retrospective cohort study"

http://www.bmj.com/content/343/bmj.d7799

"Orthopaedic surgeons: as strong as an ox and almost twice as clever? Multicentre prospective comparative study"

http://www.bmj.com/content/343/bmj.d7506

zandor• 14 years ago

For those that actually want to see how some canopies are tested then check out this video from the R&D department of Performance Designs.

http://www.youtube.com/watch?v=ERRrUcyOiE4

bicknergseng• 14 years ago

If Monty Python were allowed a medical license....

Parachute use to prevent death and major trauma due to gravitational challenge

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