On evidence (including EBM)

BMJ EBM

EBM

PICO

EBM

Challenges with EBM

Parachute use to prevent death and major trauma related to gravitational challenge: systematic review of randomised controlled trialsObjectives To determine whether parachutes are effective in preventing major trauma related to gravitational challenge. Design Systematic review of randomised controlled trials. Data sources: Medline, Web of Science, Embase, and the Cochrane Library databases; appropriate internet sites and citation lists. Study selection: Studies showing the effects of using a parachute during free fall. Main outcome measure Death or major trauma, defined as an injury severity score > 15. Results We were unable to identify any randomised controlled trials of parachute intervention. Conclusions As with many interventions intended to prevent ill health, the effectiveness of parachutes has not been subjected to rigorous evaluation by using randomised controlled trials. Advocates of evidence based medicine have criticised the adoption of interventions evaluated by using only observational data. We think that everyone might benefit if the most radical protagonists of evidence based medicine organised and participated in a double blind, randomised, placebo controlled, crossover trial of the parachute.

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Parachute use to prevent death and major trauma when jumping from aircraft: randomized controlled trialObjective To determine if using a parachute prevents death or major traumatic injury when jumping from an aircraft. Design Randomized controlled trial. Setting Private or commercial aircraft between September 2017 and August 2018. Participants 92 aircraft passengers aged 18 and over were screened for participation. 23 agreed to be enrolled and were randomized. Intervention Jumping from an aircraft (airplane or helicopter) with a parachute versus an empty backpack (unblinded). Main outcome measures Composite of death or major traumatic injury (defined by an Injury Severity Score over 15) upon impact with the ground measured immediately after landing. Results Parachute use did not significantly reduce death or major injury (0% for parachute v 0% for control; P>0.9). This finding was consistent across multiple subgroups. Compared with individuals screened but not enrolled, participants included in the study were on aircraft at significantly lower altitude (mean of 0.6 m for participants v mean of 9146 m for non-participants; P<0.001) and lower velocity (mean of 0 km/h v mean of 800 km/h; P<0.001). Conclusions Parachute use did not reduce death or major traumatic injury when jumping from aircraft in the first randomized evaluation of this intervention. However, the trial was only able to enroll participants on small stationary aircraft on the ground, suggesting cautious extrapolation to high altitude jumps. When beliefs regarding the effectiveness of an intervention exist in the community, randomized trials might selectively enroll individuals with a lower perceived likelihood of benefit, thus diminishing the applicability of the results to clinical practice.

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Reasons for unreliable evidence (cochrane)

The study may be too small to detect an effect or a difference.
The effect or difference may be very small.
There may be too few data or not enough studies.
The evidence may be of very low quality.
The studies may have been poorly designed.

Absence of evidence is not evidence of absence

Evidence of absence

https://en.wikipedia.org/wiki/Evidence_of_absence

Evidence of absence is evidence of any kind that suggests something is missing or that it does not exist.

Carl Sagan: the expression is a critique of the "impatience with ambiguity" exhibited by appeals to ignorance (something is true because it has not been proven to be false)

https://en.wikipedia.org/wiki/Argument_from_ignorance

Teapots and unicorns: absence of evidence is not evidence of absence - Evidently CochraneLynda Ware explains that absence of evidence is not evidence of absence and why it's important not to mistake one for the other, in the fourth blog in our series "Oh really? 12 things to help you question health advice." Lynda Ware explains that absence of evidence is not evidence of absence

It is difficult to prove a negative (something doesn’t exist)

The philosopher Betrand Russell: Could a tiny teapot (cosmic teapot) be orbiting the sun between Earth and Mars? This cannot be refuted.

Martin Burton (Director of Cochrane UK): wrote that an invisible unicorn had been grazing in his office and invited readers to prove him wrong!

Why do doctors use treatments that do not work?

BMJ 2004; 328 doi: https://doi.org/10.1136/bmj.328.7438.474 (Published 26 February 2004)

Cite this as: BMJ 2004;328:474

https://www.bmj.com/content/328/7438/474?sso=#:~:text=https%3A//doi.org/10.1136/bmj.328.7438.474

James Lind's did not use evidence from his own trial of citrus fruit for scurvy

Leeches and blood letting

insulin for schizophrenia and vitamin K for myocardial infarction

hormone replacement therapy does not prevent cardiovascular disease

pathophysiological reasons why β blockers are contra-indicated in heart failure (they are a good treatment for heart failure)

why colloid is more effective than crystalloid for fluid replacement (it is worse)

vascular supply of the scaphoid places it at risk of non-union, any suspected fracture requires a cast (active mobilisation results in better outcomes)

Fluoride increases bone density. But it also increases the fracture rate.

Flecainide for the treatment of supraventricular tachycardia makes the electrocardiogram look normal, but only after clinical trials (that some thought unethical) did it emerge that it increases mortality

On evidence (including EBM)

BMJ EBM

EBM

PICO

EBM

PICO

PICO

Numbers need to treat

Centre for EBM

Cochrane

EBM

Challenges with EBM

Reasons for unreliable evidence (cochrane)

Absence of evidence is not evidence of absence

Evidence of absence

Why do doctors use treatments that do not work?