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 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.