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Oh fuck *off*.

Everybody knows BMI is a shit measure anyway. Why does an entire profession, scientifically trained, ignore the evidence of the scientific method? Knowing that BMI is shit because it measures only weight with respect to height rather than anything else like bodyfat or muscle, still they persevere with it because they can't be bothered to do anything else.

Are they going to turn away athletes like Martin Johnson or Matthew Pinsent?

Cunts. Morons. I despair.

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From:

ajva.livejournal.com

I find it really difficult to know how to respond to this. It seems as if there is no possible way to proceed to try to win you over on this issue. :o)

Body composition is not routinely measured, so it is difficult to get hard statistics that I could use to further my argument. You say this:

But I can't believe the correlation is statistically insignificant either, because adiposity does affect weight, and I can't see why the other factors would exactly compensate.

But where is your evidence for other factors not "compensating", as you put it? It is based on your own anecdotal judgement:

I've known people whose weight and adiposity visibly changed in tandem, in both directions.

If there be, as you instinctively believe, some sort of positive correlation between adiposity and weight, then surely it is a correlation relating somehow to the absolute levels of fat tissue, rather than the proportional. This is all you could realistically deduce by sight, surely? Do you have X-ray Fat Vision? But the health aspect depends on the proportionality, which is in no way measured by weight, and therefore is in no way measured by BMI.

There are plenty of slim people who show up as normal on BMI measures, but have a high proportion of bodyfat; these are truly "fat", in health terms*, even if the dress/trouser size says otherwise.

* warning: Assuming a useful correlation between bodyfat percentage and healthfulness that, as I said above, may not be proven.

From:

ciphergoth.livejournal.com

It's not routinely measured, but it is sometimes measured. I googled and found this:

http://www.unu.edu/unupress/food2/UID10E/uid10e05.htm

which, interestingly, suggests that the correlation is good enough to be useful for Europeans, but less useful for non-Europeans.

From:

ergotia.livejournal.com

You are wasting your time with P on this one.

From:

djm4

But where is your evidence for other factors not "compensating", as you put it? It is based on your own anecdotal judgement:

I can't speak for

ciphergoth, but I can't think of a single other factor that would compensate in the way you'd need it to to make the correlation zero. For that, you'd need a factor that tended to make people with a higher adiposity lighter, and I don't know of one.

Just to be clear here, I'm talking about a correlation between adiposity and weight as the only two measured variables about a person. I'm not suggesting that that correlation is medically useful, nor am I suggesting that it's a 100% correlation. It won't be, because there are many other factors affecting weight. However, none of those other factors (as far as I know) produces a negative correlation between adiposity and weight, so all they do is increase the scatter about the points on the adiposity/weight graph. Which lowers the correlation, certainly, but not to zero.

But the health aspect depends on the proportionality...

Well, yes. That's what I thought you were talking about when you said that the correlation wasn't a useful measure. I agreed with that, but you seem to be saying something different here; you seem to be saying that the correlation isn't statistically significant, which is something that I doubt very much.

Note, though, that 'the correlation between adiposity and weight (or BMI for that matter) is statistically significant' is a purely mathematical judgement as far as I'm concerned. It leaves totally open the question of whether adiposity should be considered for referrals/treatment. It also leaves open the question of - given that we're talking about beople being denied access to medical help - it's justifiable to use a measure that's less than 100% correlated with the thing that we're trying to measure.

There is, I'm pretty sure, a statistically significant correlation between white-skinned people and those entitled the treatment at an NHS hospital (if you take to population of the world as a whole, I'm much less sure about the population of the UK). I would still be horrified if a doctor were to start refusing to refer someone to a hostpital based purely on the colour of their skin.

From:

djm4

There is, I'm pretty sure, a statistically significant correlation between white-skinned people and those entitled the treatment at an NHS hospital (if you take to population of the world as a whole, I'm much less sure about the population of the UK). I would still be horrified if a doctor were to start refusing to refer someone to a hostpital based purely on the colour of their skin.

Footnote - that's purely supposed to be an example if where I think it would be wrong to use even a statistically significant correlation. It wasn't meant to suggest - and I wouldn't suggest - that it's in the same league as anything anyone's suggested here.