Curbing the growth of stock trading? Order-to-trade ratios and financial transaction taxes

The growth of financial markets provokes regular debate, particularly in Europe, and in the aftermath of the global crisis a number of reforms have been proposed. In particular, two regulatory measures have been put forward: order-to-trade ratios and transaction taxes. This paper aims to quantify the impact of such initiatives. To do so, I consider market liquidity and volatility in the Italian Stock Exchange (Borsa Italiana) over the 2011-2013 period, which provides a unique opportunity for empirical assessment: first, a penalty for high order-to-trade ratios (OTR) was implemented in April 2012; second, a transaction tax on securities (STT) was introduced in March 2013 on Italian large and mid-caps; third, this tax was extended to derivatives in September 2013 (FTT). I identify causality via a difference-in-difference approach (with German firms and Italian small caps, when appropriate, as control groups) and a regression discontinuity design. I find that neither the OTR nor the STT/FTT had a meaningful impact on market liquidity or volatility. There was however a substantial drop in OTC trading.