Actually, the breakpoints for BMI are: >= 25.0 kg/m²: Overweight >= 30.0 Obese >= 35.0 Morbidly Obese Note that BMI is good for people of "normal" build but can be misleading for athletes with unusually high muscle mass. Here's a quick test: if BMI is too high AND they float, it's fat, not muscle.
It must be a holdover from when not everyone uses SI, but I feel much better when numbers (involving measurement) have units attached. It is also a great reminder of how the measure is formed; you may not need to also give the formula. ________________________________ From: Stanislav Jakuba <[email protected]> To: U.S. Metric Association <[email protected]> Cc: [email protected] Sent: Tue, August 24, 2010 4:28:09 PM Subject: [USMA:48421] BMI - a metric success The BMI (Body Mass Index) is a metrication success story because, as far as I know, the values have existed in metric only. We at the U.S.MetricAssociation should feel a measure of accomplishment. Yes, there were the feeble attempts to redefine BMI as "divide your weight in pounds times 705 by the height in inches squared" but the values were always the same. It is certainly more appealing to us to state: BMI is "your mass (kg) divided by height squared (m²)." When I incorporated the BMI calculation in my classes some 35 years ago, the numbers for the averages in the U.S. were 27.8 for man, 27.3 for women. (I wrote those numbers on the blackboard for everyone to compare theirs - a scale and a tape were provided.) But what should those numbers be? I just came across an article in Nutrition Today that reported that the ideal BMI for U.S. man is 21.9 to 22.4, say 22.2, and for women 21.3 to 22.1, say 21.7. Besides that, there is an international standard that states: Anyone 25.0 and over is obese, while anyone 18.5 and under is underweight (why not "skeletal," or something equivalently repulsive as "obese," I wonder). The article then focuses on the most interesting subject related to BMI - the beauty pageants. A survey of Miss America winners from 1922 to 1999 exhibits a more or less steady lowering of the number from 22 the first year to 18 a decade ago with a puzzling jump back to over 20 subsequently. The lowest was 16.9 in the late 1980s. As for women in the U.S., today the average is 28.4, average Miss America contestant is 19.3 and Barbie Doll is still at 13.7, unchanged since 1959. I trust you will all sleep better knowing about this metric success of kg/m². But there is more to this story. It illustrates what I have been telling my students: "With SI units only, we will not need SI units." Explaining, I would use the BMI example. And add that one may need prefixes with some values but not the unit because only one unit exists for any measurement in SI. Thus if one knows what you are talking about, such as grocery shopping in kilos, the prefix is sufficient. Everybody in the metric world knows that that kilo is kg. Now, the BMI illustrates my maxim: not even the prefix is needed. Everybody uses that number without ever seeing the unit or feeling the need for it. I bet you did not miss it in the above paragraphs. Similarly with tire pressure gages I saw in Europe - a scale only, no unit on the dial at all. Other examples exist, some not even SI related. But with SI implemented, they will be all over. Because they can be and we love them. Stan Jakuba PS: How provincial and pedantic of SI10 to preach: "Never use prefixes alone."
