Apparently Jerrold Jenkins, owner and founder of the Jenkins Group, presented the observations to a group of
small publishers using data from the Book
Industry Study Group, American Book Sellers Institute, and US News and World Report.
The diamond
industry is known for its monopsony roots where the De Beers company once controlled the distribution of all diamonds in the world, hoarding warehouses of the precious gem and only releasing a
small fraction to the market to control their high price, a practise
apparently still rampant in that
industry.