I certainly agree that BMI is not ideal, but that’s what we’ve got as far as most presently-available studies go.
In addition to all the problems that you mention with BMI, there is just systematic measurement error, which is seldom mentioned. Is the height measured with or without shoes? Do unhealthy people tend to slump rather than stand up straight, reducing their measured height, or does the person measuring height make sure to get them to stand up straight? Is weight with or without clothing? What time of day is weight measured (the morning, right after a big meal,...)? I think different answers to these questions could shift measured BMI by about 0.5, perhaps systematically for different studies. Of course, this would affect ABSI too, along with whatever similar problems there are for measuring waist circumference.
Thanks for the link to the paper on ABSI. It looks very interesting. From a first glance, it seems to support the view that the WHO “normal” category for BMI extends too far in the low direction. (Of course, using ABSI as well rather than just BMI might give better information.)
If one has measurements on height, weight, and waist circumference, and a reasonable number of subjects, I think one would actually want to look at all three measurements, not just a one or two dimensional condensation of them, using some suitably flexible model for the relationship with mortality.
I certainly agree that BMI is not ideal, but that’s what we’ve got as far as most presently-available studies go.
In addition to all the problems that you mention with BMI, there is just systematic measurement error, which is seldom mentioned. Is the height measured with or without shoes? Do unhealthy people tend to slump rather than stand up straight, reducing their measured height, or does the person measuring height make sure to get them to stand up straight? Is weight with or without clothing? What time of day is weight measured (the morning, right after a big meal,...)? I think different answers to these questions could shift measured BMI by about 0.5, perhaps systematically for different studies. Of course, this would affect ABSI too, along with whatever similar problems there are for measuring waist circumference.
Thanks for the link to the paper on ABSI. It looks very interesting. From a first glance, it seems to support the view that the WHO “normal” category for BMI extends too far in the low direction. (Of course, using ABSI as well rather than just BMI might give better information.)
If one has measurements on height, weight, and waist circumference, and a reasonable number of subjects, I think one would actually want to look at all three measurements, not just a one or two dimensional condensation of them, using some suitably flexible model for the relationship with mortality.