Using unique transactions data for individual high-frequency trading (HFT) firms in the U.K. equity market, we examine the extent to which the trading activity of individual HFT firms is correlated with each other and the impact on price efficiency. We find that HFT order flow, net positions, and total volume exhibit significantly higher commonality than those of a comparison group of investment banks. However, intraday HFT order flow commonality is associated with a permanent price impact, suggesting that commonality in HFT activity is information-based and so does not generally contribute to undue price pressure and price dislocations. Keywords: High-Frequency Trading; Correlated Trading Strategies; Price Discovery. JEL Classification: G10, G12, G14. * Benos is with the Bank of England, Threadneedle Street, London, EC2R 8AH, U.K.; Brugler is with the University of Melbourne, Department of Finance, Level 11, 198 Berkeley St, Victoria 3010, Australia; Hjalmarsson is with the University of Gothenburg, Department of Economics, Centre for Finance, Vasagatan 1, SE 405 30 Gothenburg, Sweden; and Zikes is with the Division of Financial Stability, Federal Reserve Board, 1801 K Street NW, Washington, DC 20037. Please address comments to the authors via e-mail at Evangelos. Benos@bankofengland.co.uk, james.brugler@unimelb.edu.au, erik.hjalmarsson@economics.gu.se, and Filip.Zikes@frb.gov. We are grateful to Satchit Sagade for his help in cleaning and processing the data. Helpful comments were provided by Monica Billio, Björn Hagströmer, Edwin Schooling Latter, Nick Vause, Graham Young, and seminar participants at the Bank of England, Bank of Greece, Copenhagen Business School, the Federal Reserve Board, the U.K. Financial Conduct Authority, University of Piraeus, University of York, the conference on The Development of Securities Markets: Trends, Risks and Policies at Bocconi University, the 2015 conference of the International Association of Applied Econometrics, and the 2014 Ioannina Meeting on Applied Economics and Finance. The views in this paper are solely the responsibility of the authors and should not be interpreted as representing either the views of the Bank of England or any of its committees, or the U.K.
I IntroductionHigh-frequency trading, where automated computer traders interact at lightningfast speed with electronic trading platforms, has become an important feature of many modern markets. The rapid growth and increased prominence of these ultra fast traders have given rise to concerns regarding their impact on market quality and stability. Recent events, such as the "flash crashes" in U.S. equity markets on May 6, 2010 and U.S. Treasury markets on October 15, 2014, have highlighted such worries. Over the past few years, numerous empirical studies have analyzed the market impact of high-frequency trading (HFT), as well as algorithmic trading (AT) more generally.1,2 With some recent exceptions, most of these studies have analyzed aggregate measures of HFT and AT in various markets. 3 The curre...