Posted by Milos Sugovic
Numbers are our best friend, unless of course, they’re used irresponsibly. The BMI or
body mass index is one of the most widely used (or misused) mathematical formulas out there. Why? Because it’s a formula that generates a magic number which is scientific, accurate, and easy to understand. And like most formulas, it plays a key role in decision-making. Too bad it’s
complete garbage.
Nowadays, there’s a formula or index for virtually everything out there, and like the BMI, claims accuracy beyond its statistical power. Unfortunately, the PR industry, one that has traditionally struggled with quantifying qualitative data, isn’t immune to this predisposition. So it’s important for all of us to approach “diagnostic” measures, like the BMI, with a critical eye.
One doesn’t need a course in multivariate calculus to understand why the BMI measure is nonsense. Just look at the infamous formula:
BMI = weight in pounds / (height in inches x height in inches) x 703
First of all, it leaves out measures such as waist size, as well as the importance of relative densities of muscle, bone, and fat. But let’s ignore those for a minute and assume they’re irrelevant for the sake of simplicity. Just look at the formula. Why is height in inches squared? Is there any scientific reasoning behind squaring one’s height? What about the random 703? Where did that come from?