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Physiology & Medicine / How is Body Mass Index - BMI - calculated?
« on: 08/10/2008 21:37:12 »
Listening to a program on R4 today, references to Body Mass Index said that BMI of 40 was clinically obese and for some people, 35 was reason for serious concern.
Since my body mass index is about 50 kg/m and most people think I'm a bit skinny, I'm puzzled!
I tried inverting it to get a BMI of 0.02 m/kg, but that didn't work. So perhaps they're using old fashioned imperial units: but 2.3 stone/ft doesn't work either.
In my experience, BMI is invariably referred to as an index with no units (aka a ratio?), so I wonder how this is achieved?*
Can any life scientist enlighten me?
Don.
*
The best thing that I can think of, is to compare ones mass to the mass of a lump of lard whose dimensions are related to ones height - say my mass (90kg) divided by the mass of 7.64m^3 of lard (vol=my height cubed) = 90kg / 7026kg = 0.0128 (dimensionless!)
Since this is inevitably much less than 1, I would suggest working in milliBMI's, so that would be about 13 mBMI. (If people accidentally failed to mention the unit / dimension, then it would not matter as there would be no confusion between BMI, mBMI, uBMI etc.,because the factor of 1000 would be much greater than the range of observed values.)
Since my body mass index is about 50 kg/m and most people think I'm a bit skinny, I'm puzzled!
I tried inverting it to get a BMI of 0.02 m/kg, but that didn't work. So perhaps they're using old fashioned imperial units: but 2.3 stone/ft doesn't work either.
In my experience, BMI is invariably referred to as an index with no units (aka a ratio?), so I wonder how this is achieved?*
Can any life scientist enlighten me?
Don.
*
The best thing that I can think of, is to compare ones mass to the mass of a lump of lard whose dimensions are related to ones height - say my mass (90kg) divided by the mass of 7.64m^3 of lard (vol=my height cubed) = 90kg / 7026kg = 0.0128 (dimensionless!)
Since this is inevitably much less than 1, I would suggest working in milliBMI's, so that would be about 13 mBMI. (If people accidentally failed to mention the unit / dimension, then it would not matter as there would be no confusion between BMI, mBMI, uBMI etc.,because the factor of 1000 would be much greater than the range of observed values.)