I agree that it matters who is losing the weight (that is, where in the BMI distribution they are). That’s the point I was trying to make in my 2nd paragraph. But it doesn’t matter what increment they’re losing the weight in. It makes almost no difference if a group of people all lose 2 points of BMI or if a randomly selected half of that group all lose 4 points.
If I’m reading them correctly, Paul Campos suggested that a 2 point drop in BMI was too small to make a difference, and Jonathan Graehl responded that a 2 point average drop in BMI could be big enough to matter if it results from some people having a much larger drop (which is big enough to make a difference) and others not dropping at all. My response was that any drop in BMI helps at the margin (as long as it happens to someone who is unhealthily overweight), and in the aggregate a lot of people each losing a tiny amount of weight can be just as good for public health as a smaller number of people each losing a substantial amount of weight. All that matters (if we pretend that health is solely a function of BMI) is the distribution of BMIs in the population beforehand and the distribution afterwards; it doesn’t matter which individuals are responsible for the shift in the distribution.
I agree that it matters who is losing the weight (that is, where in the BMI distribution they are). That’s the point I was trying to make in my 2nd paragraph. But it doesn’t matter what increment they’re losing the weight in. It makes almost no difference if a group of people all lose 2 points of BMI or if a randomly selected half of that group all lose 4 points.
If I’m reading them correctly, Paul Campos suggested that a 2 point drop in BMI was too small to make a difference, and Jonathan Graehl responded that a 2 point average drop in BMI could be big enough to matter if it results from some people having a much larger drop (which is big enough to make a difference) and others not dropping at all. My response was that any drop in BMI helps at the margin (as long as it happens to someone who is unhealthily overweight), and in the aggregate a lot of people each losing a tiny amount of weight can be just as good for public health as a smaller number of people each losing a substantial amount of weight. All that matters (if we pretend that health is solely a function of BMI) is the distribution of BMIs in the population beforehand and the distribution afterwards; it doesn’t matter which individuals are responsible for the shift in the distribution.