I have no actual knowledge on the topic, but I presume it's not calculated on a purely individual level. If 100 people live within the range of the local distribution warehouse are interested in this book, and they say "this one is 87% likely to buy, this one is 43% likely to but..." they can work out a model that results in very few over-shippings.
But again, I know nothing, other than thinking about it a bit when the patent app became known.
The patterns in this would be very exciting to know for people who are looking for their "tribe". It's actually something very hard to find out before moving somewhere thats not the Valley, what is the main intellectual focus of the region, is there none?
I missed a lot in my own childhood and upbringing to have people in my environment that we're or we're in contact with people at the top of their field, having deeper understanding of something instead of just struggling at their level.
But again, I know nothing, other than thinking about it a bit when the patent app became known.