Most of us on this conference are advocates of the methods of EBH and are
involved in teaching about it. How should we deal with such a major
disagreement between experts, as is currently revealed in the mammography
debate? Leaving aside the issue of harm and whether or not there is valid
evidence that surgery is increased in women undergoing mammography, what
about the main concern, mortality? On the basis of the Swedish studies
there seemed to be sufficient certainty, just a few years ago, that
mammography conferred a 25% approx. reduction in mortality. Governments
were sure enough of the validity of this evidence to initiate highly
expensive breast screening programmes as national policy. Now we have a
Cochrane metanalysis of 7 trials involving half a million women suggesting
no effect on mortality. Inadequacies are now seen in older studies that
did not appear to invalidate their results at the time.
Or is this all just the unfortunate play of chance? The earlier studies,
each on 45,000 women, were methodologically OK but just gave the wrong
results by chance? Will that wash with a sceptical audience at an
introductory EB Health Care workshop? If the evidence based
recommendations of "experts" can perform such a dramatic a U-turn on the
value of mammography, how can we trust the "concrete" evidence on
cholesterol lowering in secondary prevention of CHD, tight glycaemic and
BP control in diabetes, or anything else, they might well ask?
EBM claims to provide ordinary doctors with the ability to be able to
critically appraise evidence; to sort the wheat from the chaff. What hope
have they of accomplishing this when the professional epidemiologist and
trialist appear unable to reach agreed and consistent conclusions?
I need to sort out my own confusion on this. How do others make sense of
this and how would you simply explain it to those learning about EBM?