> The bin argument is basically saying that if the entire population gets fatter, you would expect the average weight within a bin to go up, even if some people

> The bin argument is basically saying that if the entire population gets fatter, you would expect the average weight within a bin to go up, even if some people move into the next. This depends somewhat on the shape of the curve, and the bins. But on a whole it's simply saying that the average weight of people between X lbs and Y lbs is higher than it was before. It does depend on shape of the distribution, but it is generally not the case that the average within a bin will go up. It is certainly not true for a bell curve, where if you push the curve out to the right (and flatten it), some bins will have higher averages (because they are weighted more to the right than before), but some bins will have lower averages (because they are weighted more to the left than before). If we wanted to go way deep on this, it really depends on the second derivative of the curve within a bin, not even the first derivative (a flat or even straight line through the bin will always give an average right in the middle).