Im interested to understand what is the reasoning for using the median and not average. I'm assuming the population is likely a perfect bell curve (more or less

Im interested to understand what is the reasoning for using the median and not average. I'm assuming the population is likely a perfect bell curve (more or less) in which case median would represent a higher waist size than using the average. This would seem to invalidate much of the presented thesis. I appreciate the detailed analysis of body shape, I think it is quite interesting.