The use of IQ, BMI and other quantitative indicators in health: they are neither individually significant or irrelevant. Yes, they are all important in the assessment of public – epidemic or endemic – issues, such as educational policies, hunger or obesity.
Today it is somewhat consensual that intelligence is not ONE manifestation of the human intellect, but many. The IQ is only useful, and roughly so, as a cutoff index for the design of more efficient learning environments. Otherwise, it is a poor measure of actual intelligence.
The BMI is highly useful as a measure of endemic hunger: if an adult has a BMI of under 18, in nutritional epidemiology they fall into the class of “thin adults” and, statistically, an indicator of endemic hunger. Countries or areas with over 20% of thin adults have a serious problem with hunger. The same applies to obesity. This is the indicator actually used by the World Health Organization.
The individual BMI is useless and, like the IQ, could create stigma if handled incorrectly. Dealing with teenagers, for example, it is just wrong to make these numbers known – whether publicly or privately. These are number that only matter for policy-makers.