Wait what? This isn’t even a chart of the same thing.
It’s a chart of data from 1880 to ~1980, whereas SMTM as looking specifically as the change in 1980
It’s a charge of BMI, whereas the SMTM chart is looking at growth in extreme outcomes. Say you have a normal distribution with mean 24 and SD 2. Only 0.13% of the population will have BMI over 30. But as the mean BMI slowly increases, you see rapid growth in extreme outcomes. At mean BMI of 26, you’re up to 2% over 30, at mean BMI 28 you’re up to 16%. So the fact that BMI growth is smooth doesn’t imply that obesity growth is smooth too.
It’s a chart of data from 1880 to ~1980, whereas SMTM as looking specifically as the change in 1980
The x-axis in Matthew’s chart is each cohort’s birth year, not the year their BMI was measured. Matthew’s source says the chart includes BMI data from 1959 to 2006.
It’s a charge of BMI, whereas the SMTM chart is looking at growth in extreme outcomes. Say you have a normal distribution with mean 24 and SD 2. Only 0.13% of the population will have BMI over 30. But as the mean BMI slowly increases, you see rapid growth in extreme outcomes. At mean BMI of 26, you’re up to 2% over 30, at mean BMI 28 you’re up to 16%. So the fact that BMI growth is smooth doesn’t imply that obesity growth is smooth too.
Note that it’s a chart of several BMI percentiles, not only mean or median BMI, and it shows a smooth (though accelerating) growth in the highest percentiles of BMI.
This chart of rate of change of BMI (from the same source) is instructive:
It seems that there was a mid-century slowdown in BMI growth starting with cohorts born during the Great Depression, which makes sense, and makes the 1980 acceleration seem more historically unusual than it actually is.
The BMI cutoff at 25 for overweight and 30 for obese is fairly arbitrary. People in different nations, and people in different time periods, have different standards. And we know that the effect of adiposity on lifespan and health is continuous with respect to body fat percentage, at levels higher than those characteristic of very lean bodies.
The phenomenon in need of explanation is why our wastelines got larger over time. Once we provide an explanation for that phenomenon, it’s no mystery why there is a discontinuity in the obesity chart at 1980. That’s merely an artifact of the arbitary cutoff. Overall I see no deep mystery that demands explanation above and beyond rising adiposity during the 20th century. Is it your position that we ought to be find the discontinuity at 1980 mysterious anyway?
ETA: I realize now I gave short shrift to your point about the data series ending around 1980. I actually think it’s ~1986 but it’s still hard to interpret the last six years. I’ll edit my other comment to reflect this oversight.
Wait what? This isn’t even a chart of the same thing.
It’s a chart of data from 1880 to ~1980, whereas SMTM as looking specifically as the change in 1980
It’s a charge of BMI, whereas the SMTM chart is looking at growth in extreme outcomes. Say you have a normal distribution with mean 24 and SD 2. Only 0.13% of the population will have BMI over 30. But as the mean BMI slowly increases, you see rapid growth in extreme outcomes. At mean BMI of 26, you’re up to 2% over 30, at mean BMI 28 you’re up to 16%. So the fact that BMI growth is smooth doesn’t imply that obesity growth is smooth too.
The x-axis in Matthew’s chart is each cohort’s birth year, not the year their BMI was measured. Matthew’s source says the chart includes BMI data from 1959 to 2006.
Note that it’s a chart of several BMI percentiles, not only mean or median BMI, and it shows a smooth (though accelerating) growth in the highest percentiles of BMI.
This chart of rate of change of BMI (from the same source) is instructive:
It seems that there was a mid-century slowdown in BMI growth starting with cohorts born during the Great Depression, which makes sense, and makes the 1980 acceleration seem more historically unusual than it actually is.
The BMI cutoff at 25 for overweight and 30 for obese is fairly arbitrary. People in different nations, and people in different time periods, have different standards. And we know that the effect of adiposity on lifespan and health is continuous with respect to body fat percentage, at levels higher than those characteristic of very lean bodies.
The phenomenon in need of explanation is why our wastelines got larger over time. Once we provide an explanation for that phenomenon, it’s no mystery why there is a discontinuity in the obesity chart at 1980. That’s merely an artifact of the arbitary cutoff. Overall I see no deep mystery that demands explanation above and beyond rising adiposity during the 20th century. Is it your position that we ought to be find the discontinuity at 1980 mysterious anyway?
ETA: I realize now I gave short shrift to your point about the data series ending around 1980. I actually think it’s ~1986 but it’s still hard to interpret the last six years. I’ll edit my other comment to reflect this oversight.