Abstract
In a randomized clinical trial (RCT), a group of patients, initially assembled through a mixture of deliberation (involving explicit inclusion and exclusion criteria) and serendipity (which patients happen to walk into which doctor’s clinic while the trial is in progress), are divided by some random process into an experimental group (members of which will receive the therapy under test) and a control group (members of which will receive some other treatment – perhaps placebo, perhaps the currently standard treatment for the condition at issue). In a ‘double blind’ trial neither the patient nor the clinician knows to which of the groups a particular patient belongs. The results of double blind randomized controlled trials are almost universally regarded as providing the ‘gold standard’ for evidence in medicine. Fairly extreme claims to this effect can be found in the literature. For example the statistician Tukey wrote (1977, p. 679) “almost the only source of reliable evidence [in medicine] … is that obtained from … carefully conducted randomised trials”. And the clinician Victor Herbert claimed (1977, p. 690) “…the only source of reliable evidence rising to the level of proof about the usefulness of any new therapy is that obtained from well-planned and carefully conducted randomized, and, where possible, coded (double blind) clinical trials. [Other] studies may point in a direction, but cannot be evidence as lawyers use the term evidence to mean something probative … [that is] tending to prove or actually proving”. Finally, the still very influential movement in favour of ‘Evidence Based Medicine’ (EBM) that began at McMaster University in the 1980s was initially often regarded as endorsing the claim that only RCTs provide real scientifically telling evidence.
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Notes
- 1.
A 2002 study identified no less than 40 such systems of grading evidence (Agency for Healthcare Research and Quality. 2002. Systems to rate the strength of scientific evidence. Rockville MD:AHRQ,); while a 2006 survey found 20 more (Schünemann, Holger J., Atle Fretheim and Andrew D. Oxman. 2006. Improving the use of research evidence in guideline development: 9. Grading evidence and recommendations. Health Research Policy and Systems. 4:21).
- 2.
Meta-analyses and systematic reviews are attempts to amalgamate different studies on the ‘same’ intervention into one overall result. They face many interesting methodological problems.
- 3.
- 4.
For references and an especially clear account of this argument of Fisher’s – together with an especially clear demonstration that the argument fails even on its own terms, see Howson (2000).
- 5.
So for example the Director of the UK Cochrane Centre, Mike Clarke, states on the Centre’s Web-site that “[i]n a randomised trial, the only difference between the two groups being compared is that of most interest: the intervention under investigation.” http://209.211.250.105/docs/whycc.htm. Accessed 18 December 2008.
- 6.
See in particular Worrall (2007a) and references therein.
- 7.
So for example Bartlett and colleagues who introduced ECMO as a treatment for PHSS simply switched from treating all babies admitted to their hospital (U of Michigan) with the condition with the previously standard treatment to treating all babies admitted to their hospital with ECMO. No selection! (Though certainly the issue of treatment bias is a genuine one.) See Worrall (2008).
- 8.
See Bradford Hill op. cit.
- 9.
See Worrall (2008).
- 10.
- 11.
These numbers are taken from (and my treatment influenced by) Penston (2003).
- 12.
Lancet 371, 2008, pp. 1665 and 1685.
- 13.
Rawlins (op. cit., p. 16).
- 14.
Of course ‘effectiveness’ is a tricky notion too – positive effect on the ‘target disorder’ is only part of the story, side effects need to be taken into account too.
- 15.
For details and references see Penston (2003).
- 16.
Taken from Penston op. cit.
- 17.
Figures again taken from Penston op. cit.
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Worrall, J. (2010). Do We Need Some Large, Simple Randomized Trials in Medicine?. In: Suárez, M., Dorato, M., Rédei, M. (eds) EPSA Philosophical Issues in the Sciences. Springer, Dordrecht. https://doi.org/10.1007/978-90-481-3252-2_27
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