Parachute use to prevent death and major trauma related to gravitational challenge: systematic review of randomised controlled trials
BMJ 2003; 327 doi: https://doi.org/10.1136/bmj.327.7429.1459 (Published 18 December 2003) Cite this as: BMJ 2003;327:1459
All rapid responses
Rapid responses are electronic comments to the editor. They enable our users to debate issues raised in articles published on bmj.com. A rapid response is first posted online. If you need the URL (web address) of an individual response, simply click on the response headline and copy the URL from the browser window. A proportion of responses will, after editing, be published online and in the print journal as letters, which are indexed in PubMed. Rapid responses are not indexed in PubMed and they are not journal articles. The BMJ reserves the right to remove responses which are being wilfully misrepresented as published articles or when it is brought to our attention that a response spreads misinformation.
From March 2022, the word limit for rapid responses will be 600 words not including references and author details. We will no longer post responses that exceed this limit.
The word limit for letters selected from posted responses remains 300 words.
As Christmas approaches and the BMJ is putting its midwinter edition to bed we reflect on 13 years of needless confusion around the parachute analogy. [1] When is the analogy helpful and when is it not? For example, the analogy works for tension pneumothorax which has a high risk death.[2] Prompt insertion of a needle or tube alleviates the problem with an audible hiss and an immediate, clinically evident, beneficial effect which is mechanistically explicable. We have concerns about the use of the analogy in rebuttal of the need for a randomised controlled trial of lung metastasectomy.
There has now been a randomised trial of parachutes. Researchers dropped rag dolls with and without parachutes in random order from a height of 20.83 metres and then checked to see whether the various air or water filled balloons within them were ruptured. Under their controlled test conditions the dolls with parachutes had fewer ‘organ’ injuries and fractures.[3] Despite this evidence, it is unlikely that commercial airlines would consider it worthwhile to put parachutes under the seats of passengers or crew. One reason might be that the risk of death from this cause is so low that the intervention cannot be justified but more likely is that the efficacy of parachutes under specific circumstances does not translate into general effectiveness in modern civil aviation. General awareness of the analogy is unsurprising: Smith and Pell have been cited 829 times - make that 830 now. Some readers have been misled - perhaps they didn't know it was Christmas. Analogies can be informative but need to be taken in context when making decisions on patient care.
On a radiological “now you see, it now you don’t” basis metastasectomy works but unlike dropping out of a plane, a colorectal lung metastasis is rarely if ever lethal.[4] A carefully selected small minority (≤3%) have a lung metastasectomy but during their ‘cancer journey’ they have multiple other treatments spread over years. It is impossible to distinguish the signal from the noise[6] unlike when a person falling from a plane deploys a parachute.
Reference List
1 Smith GC, Pell JP: Parachute use to prevent death and major trauma related to gravitational challenge: systematic review of randomised controlled trials. BMJ 2003;327:1459-1461.
2 Wallace A: Managing in flight emergencies. BMJ 1995;311:374-376.
3 Czorlich P, Burkhardt T, Buhk JH, Matschke J, Dreimann M, Schmidt NO, Eicker SO: Does usage of a parachute in contrast to free fall prevent major trauma?: a prospective randomised-controlled trial in rag dolls. Eur Spine J 2016;25:1349-1354.
4 Aberg T, Treasure T: Analysis of pulmonary metastasis as an indication for operation: an evidence-based approach. Eur J Cardiothorac Surg 2016;50:792-798.
5 Jawed I, Wilkerson J, Prasad V, Duffy AG, Fojo T: Colorectal Cancer Survival Gains and Novel Treatment Regimens: A Systematic Review and Analysis. JAMA Oncol 2015;1:787-795.
6 Glasziou P, Chalmers I, Rawlins M, McCulloch P: When are randomised trials unnecessary? Picking signal from noise. BMJ 2007;334:349-351.
Competing interests: No competing interests
As Christmas approaches and The BMJ is putting its midwinter edition to bed we reflect on 13 years of needless confusion around the parachute analogy. [1] When is it helpful to apply it and when is it not? For example, it applies to tension pneumothorax where there is a high and imminent likelihood of death.[2] Prompt insertion of a needle or tube alleviates the problem with an audible hiss and an immediate, clinically evident beneficial effect which is mechanistically explicable and, if before and after radiology is available, the effect can be irrefutably confirmed. Our own concern about the parachute analogy is because it is brought up in rebuttal of the need for the PulMiCC randomised controlled trial of lung metastasectomy.
There has now been a randomised trial of parachutes. Researchers dropped rag dolls with and without parachutes in random order from a height of 20.83 metres and then checked to see whether the various air or water filled balloons within them were ruptured. Under their controlled test conditions the dolls with parachutes had fewer ‘organ’ injuries and fractures.[3] In spite of this evidence, it is unlikely that commercial airlines would consider it worthwhile to put parachutes under the seats of passengers or crew. One reason might be that the risk of death from this cause is so low that the intervention cannot be justified but more likely is that the efficacy of parachutes under specific circumstances does not translate into general effectiveness in modern civil aviation. General awareness of the analogy is unsurprising: Smith and Pell have been cited 829 times (make that 830 now) and some of those readers have been seriously misled.
Analogies can lead to useful discussions, but need to be taken in context when making decisions on patient care.
On a radiological “now you see, it now you don’t” basis metastasectomy works but unlike dropping out of a plane, lung metastases are not a cause of imminent death. In fact, unlike the fall, it is not the metastasis that kills you. The careful selection of a small minority (≤3%) of all the possible candidates to be offered elective metastasectomy makes it utterly unlike dropping out of a plane and the analogy is inapplicable. In modern multimodality cancer care, repeated interventions are interspersed in the years of a patient’s cancer journey.[5] Under these circumstances, discerning the signal from the noise[6] is not as easy as seeing why people dropping out of planes for recreation are well advised to use a parachute.
Reference List
1 Smith GC, Pell JP: Parachute use to prevent death and major trauma related to gravitational challenge: systematic review of randomised controlled trials. BMJ 2003;327:1459-1461.
2 Wallace A: Managing in flight emergencies. BMJ 1995;311:374-376.
3 Czorlich P, Burkhardt T, Buhk JH, Matschke J, Dreimann M, Schmidt NO, Eicker SO: Does usage of a parachute in contrast to free fall prevent major trauma?: a prospective randomised-controlled trial in rag dolls. Eur Spine J 2016;25:1349-1354.
4 Treasure T, Mineo T, Ambrogi V, Fiorentino F: Survival is higher after repeat lung metastasectomy than after a first metastasectomy: Too good to be true? J Thorac Cardiovasc Surg 2015;149:1249-1252.
5 Jawed I, Wilkerson J, Prasad V, Duffy AG, Fojo T: Colorectal Cancer Survival Gains and Novel Treatment Regimens: A Systematic Review and Analysis. JAMA Oncol 2015;1:787-795.
6 Glasziou P, Chalmers I, Rawlins M, McCulloch P: When are randomised trials unnecessary? Picking signal from noise. BMJ 2007;334:349-351.
Competing interests: No competing interests
Dear editor,
For many years a meta-analysis written by Smith and Pell (1) and published in your journal is the keystone and most referred article when discussing that many interventions in health care have not been subjected to rigorous assessment by using randomised controlled trials. They were unable to identify randomised controlled trials whether parachutes are effective in preventing major trauma related to gravitational challenge. (1)
The authors conclude that we have the choice to accept that, under exceptional circumstances, common sense might be applied when considering the potential risks and benefits of interventions. (1) The other option according to the authors is that we continue our quest for the holy grail of exclusively evidence based interventions and preclude parachute use outside the context of a properly conducted trial.
Until today only accidental falls from height with large morbidity are reported. (2)
The survivor of the highest falls was a 23 years female from Yugoslavia and she was admitted in hospital for 16 months after this fall without parachute. Recently, a male skydiver from the US became the first to jump from a plane without a parachute or wingsuit. (3) After a free-fall of 25000 feet, he was able to land in a net spread out 200 feet above ground without any injuries. We realize that this is a case report and only Level V evidence. However, this case will probably lead to future case series and Level IV evidence. It may even open up ways for Level 1 evidence proving that a net, if not missed upon landing, is more effective for untrained skydivers compared to a parachute to prevent injury. Although it was undisputed for more than 200 years that a parachute prevents major trauma when falling from a great height, it maybe less essential than we think.
We conclude that statements made in 2003 may not be valid anymore in the future. We have to be open minded and stay critical to “old” dogmas in medicine. Issue that were common sense in the past may be less ordinary in the future.
Diederik Kempen
Michel P. J. van den Bekerom
Department of orthopedic surgery. OLVG, Amsterdam, the Netherlands
1. Smith GC, Pell JP. Parachute use to prevent death and major trauma related to gravitational challenge: systematic review of randomised controlled trials. BMJ. 2003;327(7429):1459-61
2. Highest fall survived without a parachute. In: Cunningham A. Guinness world records 2002. London: Guinness World Records, 2002.
3. http://www.nytimes.com/2016/07/31/us/skydiver-luke-aikins-without-parach...
Competing interests: No competing interests
However opinions were expressed since its publication, there is
little doubt that Smith's brilliant satire is already a much-cited classic
(1,2). Comments apart, the guy that called attention for the unwittingness
of those who took it very literally and essayed about the science of RCTs
and parachuting is cristal clear right: they should read more (in general)
and more satiric writings. Smith's work is an appeal to common sense (not
the "all doctors are right" kind of common sense, but the "common sense"
kind of common sense). Besides, it is a reflection upon the limits of any
methodology when we are in search of truth. I truly liked the suggestion
by another comment that one day we shall preferably use bayesian models to
investigate health and disease, obviating the need for the "many hundred
guineans" (they are rarely aware that they must face a 'Xerxes', anyway)
in regular RCTs. My opinion for now is that, scientists or not, general
literacy and "common sense" must be better taught for doctors. I believe
that a good beginning would be the obligatory reading and interpretation
for med students of Moliere's "Le Medecin Malgre Lui"; or should it be
modernized to Le Factuelle Medecin Malgre Lui?
References:
1. Smith G,Pell JP. Parachute use to prevent death and major trauma
related to gravitational challenge: systematic review of randomised
controlled trials. BMJ 2003;327: 1459-61.
2. Potts M, Prata N, Walsh J and Grossman A. Parachute approach to
evidence based medicine. BMJ 2006; 333:701-703.
Competing interests: No competing interests
I think the purpose of this article was just to draw attention
to the fact that EBM is not infallible and it is not an
absolute truth. It is, believe or not, possible to criticize
something even when you have faith in it. The world, as
doctors know very well, is not black and white. Yes, EBM is
the best scientific strategy we have. However, this does not
make it sacred or beyond a little criticism/mockery. If we do
not acknowledge the negative sides of EBM, then how can we
call ourselves true proponents of it?
Nit picking on the particular example the authors used is
missing the point.I'm afraid that anyone who took this article
too seriously or too literally needs to read/watch more
satire.
Thank you for this very entertaining and enlightening article.
Competing interests:
None declared
Competing interests: No competing interests
I find it odd that, with so many responses, no one has addressed the
issue of how the intended use of a trial outcome affects the choice of
methodology.
The dialogue so far assumes that the question is therepeutic: Should
a doctor recommend one therapy over another?
The reality is that another important use of randomized trials is for
regulation and insurance. Randomized trials are required for a drug to be
legal, and for a drug or procedure to be paid for by insurance. The
proper analogy to make is not whether it is sensible to use a parachute
before jumping out of an airplane in the absence of randomized trials.
The more relevant analogies are:
1) Is it proper for insurance companies to help pay for the cost of
parachutes? (For this analogy to work, we must assume that it is known
before takeoff that the plane will crash, and that it must take off
anyway.) For the answer to be "yes", we should require more proof of
efficacy than for the therapeutic question.
2) Is it proper for the government to forbid the use of parachutes
in the absence of randomized trials? For the answer to be "yes", we
should require more proof of inefficacy than for the therapeutic question.
The discussion of the parachute question has focused on the question
of effectiveness, without any mention of the regulation which (if this
were a serious medical issue) would be the main outcome of the discussion.
Likewise, many debates about controversial drugs have a clear answer
if you realize that the question being asked is not just "is this drug
effective?" but also "should use of this drug be legal?" The debate takes
place framed as if it were a debate about therapy; the results are used as
if it had been a debate about regulation; and the result is too much
regulation.
Competing interests:
None declared
Competing interests: No competing interests
Comment on: Parachute use to prevent death and major trauma related
to gravitational challenge: systematic review of randomised controlled
trials
Nibu A George
Department of Biomedical Engineering
University Medical Center Groningen and University of Groningen
9713AV Groningen, The Netherlands
e-mail: n.a.george@med.umcg.nl
Abstract
Randomised controlled trials to prove the effectiveness of a medical
intervention is not necessary if it can be proved with the help of
fundamental theoretical analysis and or with the identical problems that
are well established.
Introduction
Smith et al challenged the effectiveness of parachutes in saving
human life claiming that no controlled randomised trials have been
conducted to prove it [1]. The authors also claim that the perception that
the parachutes are a successful intervention is merely based on a casual
observation rather than a rigorous scientific analysis. In order to
support their claim the have used some reports of morbidity and mortality
associated with the failure or iatrogenic complications of the
intervention [see ref 1-4 in the above ref.]. In this paper we would like
to answer to the questions raised by the above authors using the
fundamental laws of physics.
Discussion
Reply to: Evidence based pride and observational prejudice
Based on reference 7 in the above quoted manuscript, the authors
concluded that all medical interventions justified by observational data
need verifications through randomised controlled trials. In fact the
article they quoted was referring to few different pure medical cases to
describe the biasing in data analysis. Here we like to point out few
things. First of all generalizing such reports of some selected cases and
making it a universal truth is unhealthy and challenging the entire
scientific community. Secondly, the comparing the parachute scenario with
a pure medical situation is unacceptable since the parachute jump is
rather a physical situation and it become a medical situation only if the
jump caused any physical harm to the person involved.
Reply to: Natural history of Gravitational Challenge
Based on some references, the authors claimed that the effectiveness
of an intervention needs to be judged with a non-intervention. The authors
used few manually selected cases to prove the success of free fall without
a parachute and fatal jumps involving parachutes. Ironically, the data
biasing discussed above is more applicable here. Number of people jump
every day with the help of parachutes and any successful jump is not
recorded in any medical or scientific literature, simply because it has no
significance. On the other hand, large number of people dies everyday
worldwide resulting from trauma caused by free fall from heights of few
meters to several tens of meters. In fact, here the authors approached the
present problem with a clear prejudice in their mind and consequently they
picked up some exceptional historical evidences that match their claim.
Reply to: The parachute and healthy cohort effect
The authors compared the individuals jumping from an aircraft without
a parachute as high psychiatric morbidity group relative to individuals
who perform a parachute assisted jump. But the conclusion that
parachutists enjoy the protective effect of the “healthy cohort” effect of
the group of individuals who possess less psychiatric morbidity is
absolutely baseless and challenging the commonsense of the entire
scientific community. Dragging the role of “income” and “cigarette use”
into the protection gained from scientific inventions such as parachutes
are questionable. The “healthy cohort” effect in cardiac deceases etc due
to the proper exercise, dieting, better life style etc of a group of a
individuals are not comparable to the present parachute scenario.
Reply to: The medicalisation of free fall
The authors statement of induced fear and dependency and doctors
obsession with the parachutes due to its wide spread use are also
questionable. This situation can be compared to crossing a road. Although
it is only meant to cross the road during a green signal, it could be
possible sometimes to safely cross even in red signal. But an individual
crossing during a red signal may be more nervous and cautious and this
cannot be simply neglected as an induced fear, but it is a fact that this
particular individual can harm himself or others by his act. Following a
traffic rule does not require any randomised controlled trials to prove
its effectiveness and mental and physical protection that offers to each
and every individual.
Reply to: Parachutes and military industry complex
Any technological and product development involves man power and
financial expenses and all successful industries exist simply because they
make profit from their business. Many of the widely used medical
interventions such as X-rays, radiation therapy, and many of the drugs
used for treatments have adverse short and long term side effects. But
that does not stop people from using them, even if they are aware of the
side effects. Then what is the meaning of any randomised controlled trials
to prove the success or failure rate of parachutes as a life saving
intervention.
Reply to: A call to (broken) arms
Not the common sense but simple laws of physics can prove the
effectiveness of the parachute as a life saving intervention. When a
person jumps from a height accelerates towards the earth and eventually
reaches the “terminal velocity”. For an average person this terminal
velocity is about 200km/hour and it takes only about 3 seconds to reach
the terminal velocity. The damages caused to an individual hitting the
ground at this speed is not just broken arms! Now, introducing a parachute
reduces this terminal velocity to less than 10km/hour. This is comparable
to crashing an old car without any airbags to a solid concrete wall at
200km/h and 10km/h.
Reference
1. Smith G C S and Pell J P. Parachute use to prevent death and major
trauma related to gravitational challenge: systematic review of randomised
controlled trials. British Journal of Medicine 2003; 327: 1459-1461.
Competing interests:
None declared
Competing interests: No competing interests
On one level, this is a funny article. I chuckled when I first read
it. On reflection, however, I thought "Well, maybe not," because a lot of
people have died based on physicians' arrogance about their ability to
judge the efficacy of a treatment based on theory and uncontrolled
observation.
Several high profile medical procedures that were "obviously"
effective have been shown by randomized trials to be (oops) killing people
when compared to placebo. For starters to a long list of such failed
therapies, look at antiarrhythmics for post-MI arrhythmias, prophylaxis
for T. gondii in HIV infection, and endarterectomy for carotid stenosis;
all were proven to be harmful rather than helpful in randomized trials,
and in the face of widespread opposition to even testing them against no
treatment. In theory they "had to work." But didn't.
But what the heck, let's play along. Suppose we had never seen a
parachute before. Someone proposes one and we agree it's a good idea, but
how to test it out? Human trials sound good. But what's the question? It
is not, as the author would have you believe, whether to jump out of the
plane without a parachute or with one, but rather stay in the plane or
jump with a parachute. No one was voluntarily jumping out of planes prior
to the invention of the parachute, so it wasn't to prevent a health
threat, but rather to facilitate a rapid exit from a nonviable plane.
Another weakness in this straw-man argument is that the physics of
the parachute are clear and experimentally verifiable without involving
humans, but I don't think the authors would ever suggest that human
physiology and pathology in the face of medication, radiation, or surgical
intervention is ever quite as clear and predictable, or that non-human
experience (whether observational or experimental) would ever suffice.
The author offers as an alternative to evidence-based methods the
"common sense" method, which is really the "trust me, I'm a doctor"
method. That's not worked out so well in many high profile cases (see
above, plus note the recent finding that expensive, profitable angioplasty
and coronary artery by-pass grafts are no better than simple medical
treatment of arteriosclerosis). And these are just the ones for which
careful scientists have been able to do randomized trials. Most of our
accepted therapies never have been subjected to such scrutiny, but it is
breathtaking how frequently such scrutiny reveals problems.
Thanks, but I'll stick with scientifically proven remedies.
Competing interests:
None declared
Competing interests: No competing interests
I have the following questions and comments for those more qualified
than myself to address with reference to EBM:
1) The human being is not a static machine entity, but rather a mix
of complex and adaptable systems of the physical and metaphysical wrapped
up in a skin jacket; how therefore, is it possible to hold all else equal
and move only one variable and measure the outcome and attribute that
outcome to that one variable and then apply the whole concept back to this
physical and metaphysical being in a skin jacket?
2) How is it possible to map the geometric consequences of the
treatment researched or given? For instance the introduction of the motor
vehicle 'solved' the manure pollution problem created by the use of horses
in city streets. However, the solution of the motor vehicle has gone on
to create more and greater problems than it ever solved. At the time of
the introduction of the motor vehicle it was not possible to know these
geometric consequences. Therefore what if the effect of children's
vaccines is a higher incidence of SIDS, or the lack of a protein means
that the high level of mercury in vaccines cannot be removed by some
individuals and there is a non-genetic increase in the incidence of
autism? By the way, where are the studies of safety and efficacy on any
vaccine in use today or at any time in history?
3. Health is a big dollar business, with vested interest. How is it
possible not to be influenced by the almighty dollar? If the common
Turmeric can kill HPV where is the money to be made compared to using a
patent vaccine(1)?
4. How is it possible, within the scope of EBM, to ignore the damage
of the side effects of medication and surgery? Blindness attributed to
the use of corticoid steroids? Heart muscle damage caused by the use of
lipitor type drugs? The MIMS is full of the collateral damage done by
medication. How does EBM make such damage acceptable? In terms of
surgery, how is that by removing the offending part is there a cure? In
my 12 years in practice I have seen many women present minus their
reproductive organs as a form of treatment, but never in that time have I
seen a man present with the removal of his reproductive organs as a form
of treatment. It is of course possible in the instance of a motor
vehicle, to surgically remove the cable connecting the engine’s
thermometer to the reading instrument on the dash board, however, the
cause of the over heating engine has yet to be diagnosed let alone
treated.
5. What then is EBM? A treatment that does harm and has some effect
on the target tissue? Yet who determines the levels of harm and level of
effect, and who keeps tract of all the collateral damage? Once upon a
time, I was told, that one only paid one’s physician when they were well,
and stopped paying them once they were sick. Now wouldn’t that be a shot
in the arm for preventative medicine, with those earning the most and
having the most work-free time, because they were able to keep their
patients well!
1 http://www3.interscience.wiley.com/cgi-
bin/abstract/109742042/ABSTRACT
Biochemical and Biophysical Research Communications 326, 472 (2005)
Link to abstract
International Journal of Cancer 113, 951 (2005)
Link to abstract
Journal of Biological Chemistry 279, 51163 (2004)
Link to abstract
Competing interests:
Assumption: That it is possible to stimulate the initate healing ability of the human being to what ever extent without intervention to toxic substances (drugs) and surgical removal of symptoms
Competing interests: No competing interests
Efficacy of parachute use questioned
Dear editor, With even greater interest we have reread the systematic review ‘Parachute use to prevent death and major trauma related to gravitational challenge: systematic review of randomised controlled trials’ by Smith et al.[1]. In this groundbreaking review, efficacy of parachutes use as a successful intervention was questioned because evidence for efficacy was based on anecdotal evidence only. Systematic reviews are generally thought to prevent redundant research, although sometimes they lead to increased trial activity [2 3]. Results from two recent studies may shed new light on efficacy of parachute use.
The first was a single blind randomized controlled trial (RCT); the intervention group used a parachute and subjects in the control group fell from great height without a parachute [4]. The placebo group had significantly and relevantly more head injuries, cervical trauma, thoracic trauma, lumbar trauma, pelvic trauma and more hepatic, spleen and bladder injures. Unfortunately, only study subjects were blinded for having a parachute, limiting the methodological quality of the trial. We acknowledge that this is only one randomized trial and replication is needed. Another limitation of this study was that instead of human volunteers, rag dolls were used, further limiting generalizability.
The second study involved a human volunteer. The results of this study are the first in an ’all or nothing case series’ and could potentially lead to a level of evidence 1c. The inclusion concerned a 42 year old male subject who intentionally jumped out of an airplane form a height of 25,000 ft (7,600 m) without using a parachute[5]. By aiming at a net placed just above earth level the subject survived the jump without injuries. He even felt very great right after the jump, suggesting that this intervention could potentially increase quality of life. The report did not state whether the jump was approved by a local medical ethical committee.
So how to put this new treatment option into perspective? There is only anecdotal evidence for efficacy of parachute use and parachute use is highly association with serious injuries and even death[1]. Availability of this scientifically pretty sound intervention, albeit based on a non-randomized trial, questions whether new studies that establish efficacy and safety of parachute use are necessary. An ‘all or nothing case series’ has the potential to become level 1c evidence for net use when jumping out of a plane. Which is substantially higher than parachute use as argued by Smitt et at. [1].
A new RCT with parachute use as active comparator would be unnecessary with arguments opposite to reasons mentioned by Smith et al., and possibly unethical, even for rag dolls. The review by Smith et al., retrospectively was also subject to flaws. Non-randomized studies were excluded and Smitt et al. incorrectly concluded their review with a statement that there were only two options for future research; either common sense should be applied when considering risks and benefits of parachute use or that parachute use were to be used outside the context of properly conducted trials. This statement, viewed by Smitt et al. as the only two options, reminds us that a prerequisite for progress is to keep an open mind. Smitt et al. did emphasize the importance of generalizability.
Indeed, safety of net use has only been investigated in men, not women. Generalization based on representative study populations could be called a fundamental research aim on itself. The concept of generalization simply means making a correct statement about how nature works in an individual, although extrapolating can be tricky and lead to wrong assumptions. For example, results from spill risk in women during supine versus sitting micturition can possibly be extrapolated to men. However, when standing versus sitting positions in women were to be investigated, extrapolation of results to men could lead to wrong assumptions.
The implications of this new evidence could be that individuals who intentionally jump out of a plane, should not be advised to use a parachute. Given the scarcity of data, recommendations for jumping out of a plane without parachute use should be restrained in subgroups, especially in the subgroup of women. For the sake of science, for the sake of generalizability, it would be very welcome if several women jump out of a plane without using a parachute. Unfortunately, we authors are both men, so we dare and call upon female readers to volunteer.
1. Smith GC, Pell JP. Parachute use to prevent death and major trauma related to gravitational challenge: systematic review of randomised controlled trials. BMJ 2003;327(7429):1459-61 doi: 10.1136/bmj.327.7429.1459[published Online First: Epub Date]|.
2. Habre C, Tramer MR, Popping DM, et al. Ability of a meta-analysis to prevent redundant research: systematic review of studies on pain from propofol injection. BMJ 2014;348:g5219 doi: 10.1136/bmj.g5219[published Online First: Epub Date]|.
3. Ker K, Roberts I. Exploring redundant research into the effect of tranexamic acid on surgical bleeding: further analysis of a systematic review of randomised controlled trials. BMJ open 2015;5(8):e009460 doi: 10.1136/bmjopen-2015-009460[published Online First: Epub Date]|.
4. Czorlich P, Burkhardt T, Buhk JH, et al. Does usage of a parachute in contrast to free fall prevent major trauma?: a prospective randomised-controlled trial in rag dolls. European spine journal : official publication of the European Spine Society, the European Spinal Deformity Society, and the European Section of the Cervical Spine Research Society 2016;25(5):1349-54 doi: 10.1007/s00586-016-4381-z[published Online First: Epub Date]|.
5. http://wwwguinnessworldrecordscom/news/2016/8/guinness-world-records-con...
Competing interests: No competing interests