Lanchester, John. "Scalpers Inc." Review of Flash Boys: Cracking the Money Code, by Michael Lewis. London Review of Books 36 no. 11 (2014): 7-9, http://www.lrb.co.uk/v36/n11/john-lanchester/scalpers-inc Dear Sir,

It is striking for John Lanchester to claim that those who believe high-frequency trading is a net benefit to finance (and by extension, society) "offer no data to support" their views. Aside from the fact that he presents such views in the line of climate-change deniers, rather than a perfectly respectable mainstream view in financial economics, it doesn't really seem like he has gone out looking for any data himself!

In fact there is a wide literature on the costs and benefits of HFT, much of it very recent. While Lanchester (apparently following Lewis) dismisses the claim that HFT provides liquidity as essentially apologia, a 2014 paper in The Financial Review finds that "HFT continuously provides liquidity in most situations" and "resolves temporal imbalances in order flow by providing liquidity where the public supply is insufficient, and provide a valuable service during periods of market uncertainty". [1]

And looking more broadly, a widely-cited 2013 review paper, which looks at studies that isolate and analyse the impacts of adding more HFT to markets, found that "virtually every time a market structure change results in more HFT, liquidity and market quality have improved because liquidity suppliers are better able to adjust their quotes in response to new information." [2]

There is nary a mention of price discovery in Lanchester's piece—yet economists consider this basically the whole point of markets. And many high quality studies, including a 2013 European Central Bank paper [3], find that "HFTs facilitate price efficiency by trading in the direction of permanent price changes and in the opposite direction of transitory pricing errors, both on average and on the highest volatility days".

Of course, we should all know that HFT narrows spreads. For example, a 2013 paper found that the introduction of an algorithmic-trade-limiting regulation in Canada in April 2012 drove the bid-ask spread up by 9%. [4] This, the authors say, mainly harms retail investors.

The evidence is out there, and easy to find—but not always easy to fit into the narrative of a financial thriller.

Ben Southwood London

[1] http://student.bus.olemiss.edu/files/VanNessR/Financial%20Review/Issues/May%202014%20special%20issue/Jarnecic/HFT-LSE-liquidity-provision-2014-01-09-final.docx [2] http://pages.stern.nyu.edu/~jhasbrou/Teaching/2014%20Winter%20Markets/Readings/HFT0324.pdf [3] http://www.ecb.europa.eu/pub/pdf/scpwps/ecbwp1602.pdf [4] http://qed.econ.queensu.ca/pub/faculty/milne/322/IIROC_FeeChange_submission_KM_AP3.pdf