g-78 Oct-79 0 Oct-80 -0.5 0.0% 0.2% 0.4% 0.6% 0.8% Changein tax Source: Pomeranets and Weaver, Security Transaction Taxes and Market Quality, Bank of Canada Working Paper, November 2011 Wider bid-offer spreads would result in higher transaction costs for all market participants. In their research, Oliver Wyman estim