There seems to be a confusion here between 2 debates:
(i) Are some types of evidence more 'valid' than others;
(ii) Is some evidence more 'relevant'.
The first point is about whether we should accept the 'scientific'
heirarchy - E.g. is it right to prize RCT (or RCT meta-analysis) evidence
above other forms of evidence (for example observation studies /
qualitative findings), and to 'grade' results from such evidence as 'more
valid'. Plenty written on that subject.
The second is about the importance of determining the question and then
seeking the answer - rather than the other way about. This means putting
all types of available evidence together - and being as careful and
transparent in defining a method for filling the 'gaps' as in rigourously
applying the available findings.
Heather
At 23:35 27/07/99 +0100, you wrote:
>In message <[log in to unmask]
>.edu>, Djulbegovic, Benjamin <[log in to unmask]> writes
>>So, you are saying that there is no such a thing as "hierarchy of evidence"
>>?
>>ben
>>
>As so often, Dave Sackett had it right when he wrote about "choosing the
>best research design for each question" (BMJ 1997;315:1636). The thing
>that worries me most about the hierarchy of evidence is the way it
>places the meta-analysis of RCTs at the top as though this is therefore
>the "best" evidence. It isn't. It's only the most valid experimental
>evidence (and if the extent of heterogeneity in various aspects of
>trials has been underestimated it might sometimes not even be so
>valid...).
>
>The danger is that we might assume that the most important questions are
>those that can be answered by evidence which is high in the hierarchy.
>So the question "do statins reduce cardiovascular morbidity and
>mortality in patients with raised cholesterol" might be thought a more
>valid or important question than "do people who eat a Mediterranean diet
>have a lower prevalence of ischaemic heart disease than people who eat a
>diet high in saturated fat?",or "why do poor people eat a diet high in
>saturated fat?", or "what stops people taking exercise?"
>
>Our strategy for reducing cardiovascular disease might therefore, if we
>prefer high hierarchy evidence, exclude interventions aimed at
>alleviating poverty or encouraging a healthy lifestyle "because there is
>little valid evidence that these interventions are effective"
>
>This is to take far too narrow a view, not only of what constitutes
>valid and (especially) applicable evidence, but of what health care
>consists of.
>
>The main use of hierarchies of evidence, in my view, is as a shorthand
>to link recommendations in evidence-based guidelines to the evidence, so
>that when you read the guideline you know what class of evidence has
>been used. The applicability of the evidence is related to its
>usefulness and relevance as much as to its position in the hierarchy.
>Thus qualitative evidence that people believe their children are at risk
>of developing pneumonia if they don't get antibiotics might be equally
>as useful as evidence that antibiotics don't prevent pneumonia in
>children with coughs (indeed you might find an attempt to use the latter
>very frustrating if you didn't understand the former!)
>
>Toby
>--
>Toby Lipman
>General practitioner, Newcastle upon Tyne
>Northern and Yorkshire research training fellow
>
>Tel 0191-2811060 (home), 0191-2437000 (surgery)
>
>
_______________________________________________
Heather Trickey
Research Associate
Centre for Research in Social Policy (CRSP)
Loughborough University
LE11 3TU
Tel: +44 (0)1509 223377
Fax: +44 (0)1509 213409
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