Body mass index is defined as weight in kg divided by height in meters
squared. Why is the exponent on the height 2 and not 3? If people of
all sizes tend to be about the same shape, then weight divided by
height cubed should be about the same for everyone. I can think of
two possible reasons why height squared is used:
1) Ignorance. Someone screwed up and it stuck.
2) Aspect ratio. Perhaps shorter people on average have a somewhat
more stocky build than their taller counterparts. Maybe averge
diameter is not linearly proportional to average height. If this is
correct, then there are two sub-possiblities: a) the true best fit
exponent is very close to 2; b) the true best fit exponent is say 2.4
or something, and 2 is used for ease of computation.
Of course within any height group there is a lot of variation in body
build that is not accounted for by BMI meaning BMI is not a failsafe
indicator of healthy/unhealthy weight. I am not interested in this
issue.
I have the impression that tall people (like me) have higher BMIs on
average than shorter people, and that it would be better to use an
exponent larger than 2. I would like to know if this is correct, and
if so, why 2 is used. |
