BMI
What's the goal? A numerical goal lends direction to a design problem; a ratio works to make the subjective less so. One of the best, worst and therefore most controversial metrics is Body Mass Index ( BMI ). Its utility stems from being simple to calculate: weight divided by square of height in metric units. BMI's inelegance drives detractors nuts . The most relevant criticism is that it's nonsensical. BMI uses metric units, yet the ratio remains popular only in the USA (last to metricate , along with Liberia and Myanmar) to track the obesity epidemic. Calculated as mass over crude approximation of surface area, BMI corrupts the square-cube law it's meant to mimic. What BMI does well is abstract away from normative (good / bad) toward health (healthy / unhealthy). We could all pick our favorite image above, but that's got nothing to do with health. Measuring body fat percentage or conducting active fitness tests would surely ...