Goodhart's Law applies to BMI as well you know

Goodhart’s Law is the cynical but correct observation that: “When a measure becomes a target, it ceases to be a good measure”. Originally an economic observation used to explain why Ministers declaring targets find that things don’t go quite their way - reality is ‘ornery that way.

It does though have wider application:

Fishing industry outraged by plans to ban ‘fat fishermen’

New rules that require a BMI below 35 in order to be passed fit to fish described as ‘ludicrous’ and ‘playing with people’s livelihoods’

Think on it for a moment, this is a declaration that every international prop forward is too unfit to fish. Which will be a surprise to every other international rugby player.

It does, of course, get worse than this. BMI is known to be a flawed measure. We did once have a detailed and exhaustive explanation given to us by an expert in the subject about why a volume measure like this is indeed a squared not a cubic and while it convinced us at the time we’ve thankfully forgotten it. But the point was very strongly indeed made that it’s a useful shorthand as a population measure. It is not to be used - at all - upon individuals simply because there are so many other things which determine that individual relationship between height and weight. Some people really are wider than others and for reasons nothing to do with adipose tissue.

The application of BMI to something like fitness to fish is not just turning a measure into a bad one, it’s using a measure to do what it’s expressly said not to use it for.

Of course, given that this is the British bureaucracy there is a joy to it as well. For apparently our Rolls Royce minds are unaware that fat floats and so do fat people. This being encapsulated in that common - most common in fact - observation about those with certain physiques of strategically placed adipose tissue - well, they’ll never drown, will they?

We seem to have designed our governance system to require those Rolls Royce minds and then staffed it with Trabants, which isn’t we feel quite the right way around to be doing it. We’d prefer something so simple that even a papier mache two-stroke could manage it then stick the bright people into those positions.