Does my BMI look big in this?
At some point - whether it's at the doctors, at the gym, or online - all of us have probably encountered the Body Mass Index. Body Mass Index ( BMI ) is derived from a simple mathematical formula, devised by Belgian scientist Adolphe Quetelet in the 1830s, that divides a person's weight in kilograms by their height in metres squared to arrive at an estimate of an individual's body fat. It's supposed to provide an approximate measure to help judge if someone has a healthy weight - and indicate, for instance, if they are obese. But as Nick Trefethen of Oxford University's Mathematical Institute pointed out in a recent letter to The Economist the basic formula BMI relies on is flawed: 'If all three dimensions of a human being scaled equally as they grew, then a formula of the form weight/height 3 would be appropriate. They don't! However, weight/height 2 is not realistic either,' Nick tells me. 'A better approximation to a complex reality, which is the reform I wish could be adopted, would be weight/height 2.5 . Certainly if you plot typical weights of people against their heights, the result comes out closer to height 2.5 than height 2 .
