bmj.bmjjournals.com/cgi/content/full/327/7429/1459
We imposed no language restriction and included^ any studies that entailed jumping from a height greater than^ 100 metres. The accepted intervention was a fabric device, secured^ by strings to a harness worn by the participant and released^ (either automatically or manually) during free fall with the^ purpose of limiting the rate of descent.
We chose the Mantel-Haenszel^ test to assess heterogeneity, and sensitivity and subgroup analyses^ and fixed effects weighted regression techniques to explore^ causes of heterogeneity. We selected a funnel plot to assess^ publication bias visually and Egger's and Begg's tests to test^ it quantitatively.
Parachutes reduce the risk of injury^ after gravitational challenge, but their effectiveness has not^ been proved with randomised controlled trials Credit: HULTON/GETTY ^ Discussion Evidence based pride and observational prejudice It is a truth universally acknowledged that a medical intervention^ justified by observational data must be in want of verification^ through a randomised controlled trial.
Individuals^ who use parachutes are likely to have less psychiatric morbidity^ and may also differ in key demographic factors, such as income^ and cigarette use. It follows, therefore, that the apparent^ protective effect of parachutes may be merely an example of^ the "healthy cohort" effect. Observational studies typically^ use multivariate analytical approaches, using maximum likelihood^ based modelling methods to try to adjust estimates of relative^ risk for these biases. It might be argued that the pressure exerted^ on individuals to use parachutes is yet another example of a^ natural, life enhancing experience being turned into a situation^ of fear and dependency. The parachute industry has earned billions^ of dollars for vast multinational corporations whose profits^ depend on belief in the efficacy of their product. One would^ hardly expect these vast commercial concerns to have the bravery^ to test their product in the setting of a randomised controlled^ trial.
The dependency^ we have created in our population may make recruitment of the^ unenlightened masses to such a trial difficult. GCSS drafted the manuscript but JPP deleted all the^ best jokes. Incidence, epidemiology, and occupational outcomes of thoracolumbar fractures among US Army aviators.
Circulation Home page A C Marshall and J E Lock Leaving Neverland: A Randomized Trial for Coarctation Shows Pediatric Interventional Cardiology Is Growing Up Circulation, June 28, 2005;
Psychosom Med Home page N J S Christenfeld, R P Sloan, D Carroll, and S Greenland Risk Factors, Confounding, and the Illusion of Statistical Control Psychosom Med, November 1, 2004;
Journal Watch Emergency Medicine Home page Common Sense vs. Evidence-Based Medicine: Lessons from the Parachute Journal Watch Emergency Medicine, February 17, 2004;
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