Ted Harding wrote:
>Hi Folks,
> I'm encountering conceptual problems in trying to think
> about Body Mass Index (BMI). Surely these questions
> have been discussed in the medical/physiological world,
> but I haven't come across any discussion of the issues
> raised below and would welcome pointers or comments
> from the informed!
> (...)
> My concern is whether BMI is an appropriate measure, given
> what I have set out above.
BMI is an example of sacrificing global rationality for local accuracy.
Medical decision making is troubled by uncertainty. Any index or guideline,
even if imperfect, although apparently accurate, reduces the level of
uncertainty making many decisions possible and/or helping to justify them.
In economics GDP is a very imperfect measure of development, particularly
when so called defensive spending is counted, yet it simplifies debates and
aids economic policy, although globally such measure causes
unsustainability. Many health policy targets also serve the same purpose
described as "goal shift" - the "local" index becomes more important than
global insight. Here, adjusting BMI becomes more important than more
intangible fitness and vitality. Similarly, serum cholesterol level may be a
surrogate index when oxidised cholesterol appears more important and that -
less important than overall clinical impression.
BMI may play an important role in guidelines. Indications for bariatric
surgery depend on BMI. It is interesting that slight differences in BMI
profiles of study populations might have decisive impact on HTA and
recommendations with significant financial implications.
It makes me wonder how much does the BMI definition of obesity "cost" when
compared with a more complex and more adequate one. From Ted Harding's
convincing reasoning, BMI overstates the prevalence of obesity and that
translates in qute a lot of money.
Jaroslaw Wechowski BA MB BCh PhD (econ)
Warsaw School of Economics, Poland
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