I still don’t think you’re wrong. Will is correct when he says that it is more likely someone with a BMI of 25 or lower is actually overweight than someone with a BMI of 25 or higher is just well-muscled, but that isn’t the same as estimating by eye.
The point, as I understand it, is that if you live in a country where most people are overweight, your understanding of what “overweight” is will naturally be skewed. If the average person in your home country has a BMI of 25-30, you’ll see that subconsciously as normal, and therefore you could see plenty of mildly overweight people and not think they were overweight at all—only people at even higher BMI’s would be identifiable as overweight to you.
Will is correct when he says “It is more likely someone with a BMI of 25 or lower is actually overweight than someone with a BMI of 25 or higher is just well-muscled”, but that isn’t the same as estimating by eye.
Relatively minor in this particular case, but: Please don’t claim people said things they didn’t actually say. I know you’re paraphrasing, but to me the combination of “when he says” with quote marks strongly implies a verbatim quote. It’s pretty important to clearly distinguish between those two things.
I agree “BMI gives lots of false negatives compared to more reliable measures of overweight” is not the same thing as “BMI is more prone to false negatives than by-eye estimation” – it could be that BMI underestimates overweight, but by-eye estimation underestimates it even more. It would be great to see a study comparing both BMI and by-eye estimation to a third metric (I haven’t searched for this).
But if BMI is more prone to false negatives, and less prone to false positives, than most people think, that still seems to me like prima facie evidence against the claim that the opposite (that by-eye will underestimate relative to BMI) is true.
I still don’t think you’re wrong. Will is correct when he says that it is more likely someone with a BMI of 25 or lower is actually overweight than someone with a BMI of 25 or higher is just well-muscled, but that isn’t the same as estimating by eye.
The point, as I understand it, is that if you live in a country where most people are overweight, your understanding of what “overweight” is will naturally be skewed. If the average person in your home country has a BMI of 25-30, you’ll see that subconsciously as normal, and therefore you could see plenty of mildly overweight people and not think they were overweight at all—only people at even higher BMI’s would be identifiable as overweight to you.
Relatively minor in this particular case, but: Please don’t claim people said things they didn’t actually say. I know you’re paraphrasing, but to me the combination of “when he says” with quote marks strongly implies a verbatim quote. It’s pretty important to clearly distinguish between those two things.
Fair enough. I’ve edited it to remove the quotation marks.
I agree “BMI gives lots of false negatives compared to more reliable measures of overweight” is not the same thing as “BMI is more prone to false negatives than by-eye estimation” – it could be that BMI underestimates overweight, but by-eye estimation underestimates it even more. It would be great to see a study comparing both BMI and by-eye estimation to a third metric (I haven’t searched for this).
But if BMI is more prone to false negatives, and less prone to false positives, than most people think, that still seems to me like prima facie evidence against the claim that the opposite (that by-eye will underestimate relative to BMI) is true.