Fragmentation and Price Discovery : A Comparison of Reg NMS and MiFID1

We study NYSE, NASDAQ, and ARCA prices for DJIA stocks and LSE, Xetra, and Chi-X prices for five leading British equities. MiFID1 hastened fragmentation but accomplished the intended cointegration of European equity markets that had previously been segmented. Initially, price discovery in London was largely unaffected; permanent quote innovations remained more than ninety percent attributable to the LSE. However, clearing and settlement fee reductions by Chi-X five months later did result in a substantial reduction in the information impounding and price discovery efficiency of London Stock Exchange trades. The contemporaneous situation in the U.S. with the implementation of Reg NMS was quite different. During its staggered rollout in 2007, NYSE's price discovery declined steadily from 74% to 41% with much of that role migrating to ARCA. In this case, the price discovery efficiency of NASDAQ substantially improved