> questions about the determination of scientific consensus...

Is it accurate to take a situation that is unique to 
medicine/health and label it as a generalized "problem
of scientific consensus" for science as a whole?

Not at all.

Of course the problem(s) with medical science (and the 
reporting of it to the public) are many and severe.  
As an example, think quick - is milk supposed to be 
"good" or "bad" for you this week?

The basic difficulty with medical studies is that it would 
be very unethical to do the sort of "controlled studies" 
where the controls all die as a result of a lack of a 
specific treatment.

Another big problem turns out to be that there are simply too
many factors to account for, even when one attempts to do a
clean single-variable study, as opposed to the much less
credible "cohort studies".

A broad overview of these issues can be found in the "Magazine"
section of Sunday's NYTimes: 

http://www.nytimes.com/2007/09/16/magazine/16epidemiology-t.html?ref=mag
azine

The editorial mentioned in the article, "Epidemiology-is it time to call
it a day?", 
published in the International Journal of Epidemiology (Jan 2001) is
here:

http://ije.oxfordjournals.org/cgi/content/full/30/1/1

Note that even the original case of Cholera, it is now generally thought
that removing the pump handle from the communal pump had little or
nothing to do with stopping the Cholera epidemic.  

The general case for medical science is that there are simply 
too many people, too many journals, not enough time.  

Here's an editorial from "Nature" in 2002:
http://www.nature.com/neuro/journal/v5/n12/full/nn1202-1249.html

"Looking at the] Medline database from 1966 to 1997 
revealed that of the nine million or so articles 
indexed during this period, only 235 were retracted - 
in other words, less than 0.01%. (As of this writing, 
the numbers have risen to over twelve million articles 
and 464 retractions.) 

Unfortunately, however, retraction alone does not appear 
sufficient as a way to clean up the scientific literature, 
because articles often continue to be cited after they 
have been retracted. For example, the 235 retracted papers 
in the survey above received more than 2000 citations, of 
which the great majority presented the conclusions as if 
they were still valid."


So, everything you "know" is wrong, everything your teacher told
you, other than math, was lies, and we had all better start every
morning with "I think, therefore I am", and hope we can all work
fast enough to individually reinvent Calculus by lunchtime, so we 
can get some actual work done in the afternoons.

Or we can wake up, navigate the terrain as we see it, and simply
remember that there may be land mines out there.

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