Retrieved 25 December 2011. ↑ Brynjolfsson, Erik; Yu (Jeffrey) Hu, and Michael D. Smith, "Consumer Surplus in the Digital Economy: Estimating the Value of Increased Product Variety at Online Booksellers", Management Science, 49 (11), November 2003. working paper version, April 2003 ↑ Bynjolfsson, Erik; Yu (Jeffrey) Hu, and Michael D. Smith, 2010, "The Longer Tail: The Changing Shape of Amazon’s Sales Distribution Curve" ↑ Brynjolfsson, Erik; Yu (Jeffrey) Hu, and Duncan Simester, 2006, "Goodbye Pareto Principle, Hello Long Tail: The Effect of Search Costs on the Concentration of Product Sales" ↑ Brynjolfsson, Erik; Hu, Yu Jeffrey; Smith, Michael D.