RCTs and parachutes

In the tight-sphinctered world of academic medicine, it's always delightful to find a journal that still has a sense of humor. The following satirical paper from the British Journal of Medicine made me laugh and laugh.Smith GCS, Pell JP. (2003). Parachute use to prevent death and major trauma related to gravitational challenge: systematic review of randomised controlled trials. BMJ, 327(7429), 1459-1461. DOI: 10.1136/bmj.327.7429.1459
In a nutshell, this paper rightfully points out that no one has ever done a randomized, controlled trial (RCT) on the efficacy of parachutes. Furthermore,

Advocates of evidence-based medicine have criticised the adoption of interventions evaluated by using only observational data.

To be funny, satire has to contain enough truth about its subject to properly skewer its underlying fallacies. Smith and Pell's excellent paper carries the concept of parachute efficacy through the usual machinery of evidence-based medicine, all the way to the following hilarious reductio ad absurdum conclusion:

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.

From skimming through the comments stimulated by this paper, it seems that not all of the BMJ readers recognized it as satire, even though the article concludes with the following contributors' statement:

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.

A Bit More on Evidence-Based Medicine

The formal term "evidence-based medicine" (EBM), is a relative newcomer on the medical research scene, and is based on early publications by Cochrane in 1972 and Sackett and Guyatt in the early 1990's. Their idea is a simple one: make clinical decisions based on a synthesis of the best available evidence about a treatment.

Just a few decades later, there are way many EBM advocates who are way too ready to blindly wield EBM like a mighty sword without understanding its limitations. IMHO, one of its biggest limitations is the current EBM definition of "best available evidence". For example, consider the Oxford Centre for Evidence-based Medicine Levels of Evidence (May 2001):

Level Therapy/Prevention, Aetiology/Harm
1a systematic review (with homogeneity*) of RCTs
1b Individual RCT (with narrow Confidence Interval‡)
1c All or none§
2a systematic review (with homogeneity*) of cohort studies
2b Individual cohort study (including low quality RCT; e.g., <80%>Oscillococcinum). However, the solutions usually employed are so dilute there is not a single molecule left of the original agent. Scientific likelihood of any benefit over that of plain water = zip.
Homeopathy counters this with the claim that the diluting water has a "memory" of the original agent, even though it's all gone. However, there is no scientific evidence of such a "memory" effect. Besides, when one considers how much of our planet's water passes through human kidneys, it seems likely that any possible "memory" of Oscillococcinum would be swamped by just the "memory" of used beer.

Bottom line: scientific likelihood of any benefit of homeopathy over that of plain water again = zero/zed/zip.

In this case, the basic science is so overwhelmingly against any benefit that it seems ridiculous to perform an RCT of homeopathic claims. Even if a marginally weak effect were suggested by a clinical trial, the a priori implausibility of homeopathy makes it hard to put much confidence in the result.
Parachutes
The physics of falling bodies, on the other hand, has been understood for a long time, particularly when there is atmospheric drag. The terminal velocity of a falling human in air is about 55 m/s (120 mph). Scientific likelihood of survival = almost 0% (a few fluke cases have been reported of lucky folks surviving parachute failures).
A properly designed parachute can decrease this falling speed to as little as 2.1 m/s, about the speed you'd develop by jumping off a 9 inch stool. Scientific likelihood of survival = virtually 100%.

In this case, the basic science is overwhelmingly in favor of survival. Therefore, I'm willing to take my chances with a parachute during my next plunge from a height -- RCT or no RCT.
Syndicated from samurai radiologist.