Dear colleagues,
A bit surprised with the silence of this discussion group, I want to draw
your attention to June 22 issue of New England Journal of Medicine where two
papers challenged a central tenet of EBM, which is that the validity of
evidence is a function of the design of the study from which the finding is
collected. Hence, supremacy of randomized trials as "gold standard" of truth
was questioned.
In my opinion, the question of hierarchy of medical evidence represents a
core issue of EBM movement and if indeed assumption that "not all evidence
is created equal" is not accepted then there is not much left of the EBM
paradigm. This is an issue that my colleagues and I have given a lot of
thoughts during last several years and tried to answer in several papers and
commentaries in various ways. However, the more I think about it, the more
it appears that the question of superiority of RCTs vs. observational
studies is PERHAPS empirically an unanswerable question. For the simple
reason of the lack of "standard of truth". Current, hierarchy of evidence is
NORMATIVELY derived, and reflects belief in supremacy of experimental method
that has served us so well
over such a long period of time. However, as I just stated, this hypothesis
that experimental method is superior to observational one appears not to be
empirically testable [much as normative models of decision making (dealing
with the question how should we make decisions) cannot be shown to be
superior to descriptive models of decision making (dealing with the question
how we actually make decisions)]. As postmodernists would say real life
defies the precision of normative, mathematically ordained world; the truth
is elusive and subjective. In deciding what works and what doesn't should we
then add a "value factor" to each form of scientific evidence? Or, hierarchy
of findings closest to the truth should be looked across all forms of
evidence relevant to particular question at hand, as suggested by E.
Wilson's consilience model. According to this view the 'consilience test'
takes place when findings obtained from one class of facts coincides with
findings obtained from another different class of observations.
Could it be that the current hierarchy of evidence is just not sufficiently
good enough or that ranking of evidence is not a feasible exercise to begin
with?
These are crucial issues to whole idea of EBM, and it would be interesting
to hear opinions from the members of the group about relative value of
experimental method vs. observational one and whether creation of hierarchy
of medical evidence is a feasible idea.
Ben Djulbegovic
P.S. At some point in the past, I tried to survey members of the group with
respect to the Oxford grading of level of evidence (see:
http://cebm.jr2.ox.ac.uk/docs/levels.html). The majority respondents agreed
with the Oxford ranking of evidence. Should this ranking be redefined in
light of the NEJM articles?
Benjamin Djulbegovic, MD,PhD
Associate Professor of Medicine
H. Lee Moffitt Cancer Center & Research Institute
at the University of South Florida
Division of Blood and Bone Marrow Transplant
12902 Magnolia Drive
Tampa, FL 33612
Editor: Evidence-based Oncology
http://www.harcourt-international.com/journals/ebon/
e-mail:[log in to unmask]
http://www.hsc.usf.edu/~bdjulbeg/
phone:(813)979-7202
fax:(813)979-3071
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