Part 2 of the article:
Well that at least explains the 703. Sort of. But given that the formula is self-evidently just a kludge, why not round it to 700. Stating it as 703 gives an air of accuracy the formula cannot possibly merit, and suggests that the folks who promote this piece of numerological nonsense either have no real understanding of numbers or they want to blind us by what they think we will accept as science.
Another question: Why is the original metric formula expressed in terms of kilograms and meters? Why not grams and centimeters? Or some other units? Well, given the scientific absurdity of dividing someone's weight by the square of their height it really doesn't matter what the units are. I suspect the ones chosen were so that the resulting number comes out between 1 and 100, and thus looks reassuringly like a percentage. I'm beginning to suspect my "blind-us-with-science" conspiracy theory may be right after all.
So which clown first dreamt up this formula and why? Well, it was actually no clown at all, but one of the smartest mathematicians in history: the Belgian polymath Lambert Adolphe Jacques Quetelet (1796 - 1874). Quetelet received a doctorate in mathematics from the University of Ghent in 1819, and went on to do world class work in mathematics, astronomy, statistics, and sociology. Indeed, he was one of the founders of both these last two disciplines, being arguably the first person to use statistical methods to draw conclusions about societies.
It is to Quetelet that we can trace back that important figure in twentieth century society, the "average man." (You know, the one with 2.4 children.) He (Quetelet, not the average man) realized that the most efficient way to organize society, allocate resources, etc. was to count and measure the population, using statistical methods to determine the (appropriate) "averages". He looked for mathematical formulas that would correlate, numerically, with those "average citizens."
(Elementary) statistics being the highly simplistic (but extremely powerful) tool that it is, it is generally not difficult to find simple formulas that correlate pretty well with society's averages. You just play around with a few variables until you find a formula that fits. If you can provide a scientific rationale for the formula, so much the better, and you are justified in having more confidence in your ability to use the formula predictively. But it is generally enough that your formula is empirically representative. Provided that all you are doing is trying to draw conclusions about society as a whole, that is. Quetelet knew what he was doing. Many since then, including, it appears, the CDC, do not.
The absurdity of using statistical formulas to make any claim about a single individual is made clear by the old joke about the man who had his head in the refrigerator and his feet in the fire: on average he felt fine!
Yet the CDC says, on its website,
"BMI is a reliable indicator of body fatness for people."
Nonsense. It is off-the-charts unreliable for me and for millions of people like me. True, a few sentences later, the CDC - doubtless at the insistence of their lawyers - says
"However, BMI is not a diagnostic tool."
You're telling me! Come on guys, either the BMI is, as you claim, "a reliable indicator of body fatness", in which case you can so use it, or, as you also admit, it cannot be used to diagnose excess body fat. Which is it to be?
The CDC's answer becomes clear as we read on. Lest we note the disclaimer that the BMI cannot be used to diagnose excess body fat and demand a more reliable procedure, they immediately go on to mask their legal get-out by claiming,
"Calculating BMI is one of the best methods for population assessment of overweight and obesity. Because calculation requires only height and weight, it is inexpensive and easy to use for clinicians and for the general public. The use of BMI allows people to compare their own weight status to that of the general population."
I'll say it again. This statement is completely false; there are several much better methods - some of which the CDC actually lists on its website! The only part of this second statement that I see as having any validity is the very telling admission that the BMI method is inexpensive and easy to use.
There is another problem with the manner in which the CDC and other medical authorities explain the BMI. Notice that the interpretive ranges into the categories underweight, ideal, etc. are given to one decimal place, with equal signs. This suggests a level of precision in the formula that cannot possibly be warranted. (Some sites give two decimal places.) It would at least be more honest to give the ranges like this:
below 19 you are likely to be underweight
between 19 and 25 is the range generally viewed as ideal
between 25 and 30 suggests you may be overweight
if you are above 30 you are likely to be obese
This would not make the formula any less a piece of numerological junk, but at least would indicate that the ranges are just rough guidelines. The only possible reason for giving the ranges in the precise way the CDC does is to try to mislead patients that there is something scientific going on here. It's a classic example of "lying with numbers."
So here is the beef (lean, of course). The BMI was formulated, by a mathematician, not a medical physician, to provide a simple, easy-to-apply mathematical formula to give a broad, society-level measure of weight issues. It has absolutely no scientific or medical basis. It is based purely on a crude statistical analysis. It measures a general society trend, it does not predict. Since the majority of people today (and in Quetelet's time) lead fairly sedentary lives, and are not particularly active, the formula tacitly assumes low muscle mass and high relative fat content. It applies moderately well when applied to such people because it was formulated by focusing on them! Duh!
But this is not science - it's not even good statistics - and as a result it should not be accepted medical practice, to be regularly flouted as some magical mumbo jumbo and used as a basis for giving advice to patients. (For heavens sake, even seven times Tour de France winner Lance Armstrong's own Livestrong website provides a BMI calculator, despite the fact that the boss himself, when he first became a world champion cyclist - before chemotherapy for cancer took 20lbs off him - found himself classified as "overweight" by the wretched formula.)
As you might expect, once a piece of numerological nonsense is held up for proper scrutiny, it doesn't take long before the whole house of cards comes tumbling down. The surprising thing about the BMI is that it has survived for so long (as a diagnostic for individual patients). As I indicated earlier, I suspect that much of the appeal is that it is a single number, easy to calculate, given an air of scientific authority by a mathematical formula, and (just as my earlier quote from the CDC makes clear) it is easier and quicker to base a diagnosis on a number than on properly examining a patient. But at that point you have stopped doing medicine and are just doing kindergarten arithmetic.
Well that at least explains the 703. Sort of. But given that the formula is self-evidently just a kludge, why not round it to 700. Stating it as 703 gives an air of accuracy the formula cannot possibly merit, and suggests that the folks who promote this piece of numerological nonsense either have no real understanding of numbers or they want to blind us by what they think we will accept as science.
Another question: Why is the original metric formula expressed in terms of kilograms and meters? Why not grams and centimeters? Or some other units? Well, given the scientific absurdity of dividing someone's weight by the square of their height it really doesn't matter what the units are. I suspect the ones chosen were so that the resulting number comes out between 1 and 100, and thus looks reassuringly like a percentage. I'm beginning to suspect my "blind-us-with-science" conspiracy theory may be right after all.
So which clown first dreamt up this formula and why? Well, it was actually no clown at all, but one of the smartest mathematicians in history: the Belgian polymath Lambert Adolphe Jacques Quetelet (1796 - 1874). Quetelet received a doctorate in mathematics from the University of Ghent in 1819, and went on to do world class work in mathematics, astronomy, statistics, and sociology. Indeed, he was one of the founders of both these last two disciplines, being arguably the first person to use statistical methods to draw conclusions about societies.
It is to Quetelet that we can trace back that important figure in twentieth century society, the "average man." (You know, the one with 2.4 children.) He (Quetelet, not the average man) realized that the most efficient way to organize society, allocate resources, etc. was to count and measure the population, using statistical methods to determine the (appropriate) "averages". He looked for mathematical formulas that would correlate, numerically, with those "average citizens."
(Elementary) statistics being the highly simplistic (but extremely powerful) tool that it is, it is generally not difficult to find simple formulas that correlate pretty well with society's averages. You just play around with a few variables until you find a formula that fits. If you can provide a scientific rationale for the formula, so much the better, and you are justified in having more confidence in your ability to use the formula predictively. But it is generally enough that your formula is empirically representative. Provided that all you are doing is trying to draw conclusions about society as a whole, that is. Quetelet knew what he was doing. Many since then, including, it appears, the CDC, do not.
The absurdity of using statistical formulas to make any claim about a single individual is made clear by the old joke about the man who had his head in the refrigerator and his feet in the fire: on average he felt fine!
Yet the CDC says, on its website,
"BMI is a reliable indicator of body fatness for people."
Nonsense. It is off-the-charts unreliable for me and for millions of people like me. True, a few sentences later, the CDC - doubtless at the insistence of their lawyers - says
"However, BMI is not a diagnostic tool."
You're telling me! Come on guys, either the BMI is, as you claim, "a reliable indicator of body fatness", in which case you can so use it, or, as you also admit, it cannot be used to diagnose excess body fat. Which is it to be?
The CDC's answer becomes clear as we read on. Lest we note the disclaimer that the BMI cannot be used to diagnose excess body fat and demand a more reliable procedure, they immediately go on to mask their legal get-out by claiming,
"Calculating BMI is one of the best methods for population assessment of overweight and obesity. Because calculation requires only height and weight, it is inexpensive and easy to use for clinicians and for the general public. The use of BMI allows people to compare their own weight status to that of the general population."
I'll say it again. This statement is completely false; there are several much better methods - some of which the CDC actually lists on its website! The only part of this second statement that I see as having any validity is the very telling admission that the BMI method is inexpensive and easy to use.
There is another problem with the manner in which the CDC and other medical authorities explain the BMI. Notice that the interpretive ranges into the categories underweight, ideal, etc. are given to one decimal place, with equal signs. This suggests a level of precision in the formula that cannot possibly be warranted. (Some sites give two decimal places.) It would at least be more honest to give the ranges like this:
below 19 you are likely to be underweight
between 19 and 25 is the range generally viewed as ideal
between 25 and 30 suggests you may be overweight
if you are above 30 you are likely to be obese
This would not make the formula any less a piece of numerological junk, but at least would indicate that the ranges are just rough guidelines. The only possible reason for giving the ranges in the precise way the CDC does is to try to mislead patients that there is something scientific going on here. It's a classic example of "lying with numbers."
So here is the beef (lean, of course). The BMI was formulated, by a mathematician, not a medical physician, to provide a simple, easy-to-apply mathematical formula to give a broad, society-level measure of weight issues. It has absolutely no scientific or medical basis. It is based purely on a crude statistical analysis. It measures a general society trend, it does not predict. Since the majority of people today (and in Quetelet's time) lead fairly sedentary lives, and are not particularly active, the formula tacitly assumes low muscle mass and high relative fat content. It applies moderately well when applied to such people because it was formulated by focusing on them! Duh!
But this is not science - it's not even good statistics - and as a result it should not be accepted medical practice, to be regularly flouted as some magical mumbo jumbo and used as a basis for giving advice to patients. (For heavens sake, even seven times Tour de France winner Lance Armstrong's own Livestrong website provides a BMI calculator, despite the fact that the boss himself, when he first became a world champion cyclist - before chemotherapy for cancer took 20lbs off him - found himself classified as "overweight" by the wretched formula.)
As you might expect, once a piece of numerological nonsense is held up for proper scrutiny, it doesn't take long before the whole house of cards comes tumbling down. The surprising thing about the BMI is that it has survived for so long (as a diagnostic for individual patients). As I indicated earlier, I suspect that much of the appeal is that it is a single number, easy to calculate, given an air of scientific authority by a mathematical formula, and (just as my earlier quote from the CDC makes clear) it is easier and quicker to base a diagnosis on a number than on properly examining a patient. But at that point you have stopped doing medicine and are just doing kindergarten arithmetic.
