Dark Pools, Fragmented Markets, and the Quality of Price Discovery

This commentary is on a paper published in 2010. Few would wish to roll the markets back to where they were eight years ago, but have the issues that were debated then been adequately resolved? Are today’s markets acceptably efficient? Can we relax about market quality? My answer to each of these is “no.” What I wrote in 2010, I stand by now. Along with revisiting my previous discussion on dark pools, fragmentation, price discovery, and liquidity, this commentary presents my newer thoughts concerning the definition of the term “liquidity,” and the existence of an illiquidity premium.